johnson-nyquist thermal noise by: mohammad ali ahmadi pajouh aut 2007
TRANSCRIPT
Johnson-Nyquist Thermal Noise
By Mohammad Ali Ahmadi Pajouh
AUT 2007
Some Interesting Measurements
Noise
bull Noise is a complex composite of lots of things
1 Thermal or Johnson Noise2 Shot noise
3 Flicker or 1f noise
4 Environmental noise
History
bull In 1927 J B Johnson observed random fluctuations in the voltages across electrical resistors A year later H Nyquist published a theoretical analysis of this noise which is thermal in origin Hence this type of noise is variously called Johnson noise Nyquist noise or Thermal noise
bull At any non-zero temperature we can think of the moving charges as a sort of Electron Gas trapped inside the resistor box
bull The electrons move about in a randomised way mdash similar to Brownian motion mdash bouncing and scattering off one another and the atoms
bull At any particular instant there may be more electrons near one end of the box than the other
bull If we note the meter reading at regular intervals (eg every second) for a long period we can plot a histogram of the results
bull we choose a lsquobin widthrsquo dv and divide up the range of possible voltages into small lsquobinsrsquo of this size We then count up how often the measured voltage was in each bin divide those counts by the total number of measurements and plot a histogram
bull We can now use this plot to indicate the likelihood or probability that any future measurement of the voltage will give a result in any particular small range
bull NYQUIST EQUATION
bull ltV2gt = 4kTRf
For frequencies below a few gigahertz Equation 1 gives the relationship between the- ltV2gt the measured mean-squared voltage - (T) absolute temperature of the resistor - ( R) its resistance - f is the bandwidth in hertz over which the noise is measured For a resistor of 1kΩ at room temperature and a 10 kHz bandwidth the RMS noise voltage is 400 nV or 04 microvolts - kB is Boltzmanrsquos constant (138 x 10-23- JoulesKelvin)
POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONSbull The frequency content of the random fluctuations are characterized by the power spectral density (PSD)bull PSD = power per unit frequencybull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoisebull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1
- f2 ) where(f1 - f2) is the bandwidth of the measurement systembullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
Some Interesting Measurements
Noise
bull Noise is a complex composite of lots of things
1 Thermal or Johnson Noise2 Shot noise
3 Flicker or 1f noise
4 Environmental noise
History
bull In 1927 J B Johnson observed random fluctuations in the voltages across electrical resistors A year later H Nyquist published a theoretical analysis of this noise which is thermal in origin Hence this type of noise is variously called Johnson noise Nyquist noise or Thermal noise
bull At any non-zero temperature we can think of the moving charges as a sort of Electron Gas trapped inside the resistor box
bull The electrons move about in a randomised way mdash similar to Brownian motion mdash bouncing and scattering off one another and the atoms
bull At any particular instant there may be more electrons near one end of the box than the other
bull If we note the meter reading at regular intervals (eg every second) for a long period we can plot a histogram of the results
bull we choose a lsquobin widthrsquo dv and divide up the range of possible voltages into small lsquobinsrsquo of this size We then count up how often the measured voltage was in each bin divide those counts by the total number of measurements and plot a histogram
bull We can now use this plot to indicate the likelihood or probability that any future measurement of the voltage will give a result in any particular small range
bull NYQUIST EQUATION
bull ltV2gt = 4kTRf
For frequencies below a few gigahertz Equation 1 gives the relationship between the- ltV2gt the measured mean-squared voltage - (T) absolute temperature of the resistor - ( R) its resistance - f is the bandwidth in hertz over which the noise is measured For a resistor of 1kΩ at room temperature and a 10 kHz bandwidth the RMS noise voltage is 400 nV or 04 microvolts - kB is Boltzmanrsquos constant (138 x 10-23- JoulesKelvin)
POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONSbull The frequency content of the random fluctuations are characterized by the power spectral density (PSD)bull PSD = power per unit frequencybull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoisebull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1
- f2 ) where(f1 - f2) is the bandwidth of the measurement systembullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
Noise
bull Noise is a complex composite of lots of things
1 Thermal or Johnson Noise2 Shot noise
3 Flicker or 1f noise
4 Environmental noise
History
bull In 1927 J B Johnson observed random fluctuations in the voltages across electrical resistors A year later H Nyquist published a theoretical analysis of this noise which is thermal in origin Hence this type of noise is variously called Johnson noise Nyquist noise or Thermal noise
bull At any non-zero temperature we can think of the moving charges as a sort of Electron Gas trapped inside the resistor box
bull The electrons move about in a randomised way mdash similar to Brownian motion mdash bouncing and scattering off one another and the atoms
bull At any particular instant there may be more electrons near one end of the box than the other
bull If we note the meter reading at regular intervals (eg every second) for a long period we can plot a histogram of the results
bull we choose a lsquobin widthrsquo dv and divide up the range of possible voltages into small lsquobinsrsquo of this size We then count up how often the measured voltage was in each bin divide those counts by the total number of measurements and plot a histogram
bull We can now use this plot to indicate the likelihood or probability that any future measurement of the voltage will give a result in any particular small range
bull NYQUIST EQUATION
bull ltV2gt = 4kTRf
For frequencies below a few gigahertz Equation 1 gives the relationship between the- ltV2gt the measured mean-squared voltage - (T) absolute temperature of the resistor - ( R) its resistance - f is the bandwidth in hertz over which the noise is measured For a resistor of 1kΩ at room temperature and a 10 kHz bandwidth the RMS noise voltage is 400 nV or 04 microvolts - kB is Boltzmanrsquos constant (138 x 10-23- JoulesKelvin)
POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONSbull The frequency content of the random fluctuations are characterized by the power spectral density (PSD)bull PSD = power per unit frequencybull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoisebull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1
- f2 ) where(f1 - f2) is the bandwidth of the measurement systembullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
History
bull In 1927 J B Johnson observed random fluctuations in the voltages across electrical resistors A year later H Nyquist published a theoretical analysis of this noise which is thermal in origin Hence this type of noise is variously called Johnson noise Nyquist noise or Thermal noise
bull At any non-zero temperature we can think of the moving charges as a sort of Electron Gas trapped inside the resistor box
bull The electrons move about in a randomised way mdash similar to Brownian motion mdash bouncing and scattering off one another and the atoms
bull At any particular instant there may be more electrons near one end of the box than the other
bull If we note the meter reading at regular intervals (eg every second) for a long period we can plot a histogram of the results
bull we choose a lsquobin widthrsquo dv and divide up the range of possible voltages into small lsquobinsrsquo of this size We then count up how often the measured voltage was in each bin divide those counts by the total number of measurements and plot a histogram
bull We can now use this plot to indicate the likelihood or probability that any future measurement of the voltage will give a result in any particular small range
bull NYQUIST EQUATION
bull ltV2gt = 4kTRf
For frequencies below a few gigahertz Equation 1 gives the relationship between the- ltV2gt the measured mean-squared voltage - (T) absolute temperature of the resistor - ( R) its resistance - f is the bandwidth in hertz over which the noise is measured For a resistor of 1kΩ at room temperature and a 10 kHz bandwidth the RMS noise voltage is 400 nV or 04 microvolts - kB is Boltzmanrsquos constant (138 x 10-23- JoulesKelvin)
POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONSbull The frequency content of the random fluctuations are characterized by the power spectral density (PSD)bull PSD = power per unit frequencybull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoisebull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1
- f2 ) where(f1 - f2) is the bandwidth of the measurement systembullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
bull At any non-zero temperature we can think of the moving charges as a sort of Electron Gas trapped inside the resistor box
bull The electrons move about in a randomised way mdash similar to Brownian motion mdash bouncing and scattering off one another and the atoms
bull At any particular instant there may be more electrons near one end of the box than the other
bull If we note the meter reading at regular intervals (eg every second) for a long period we can plot a histogram of the results
bull we choose a lsquobin widthrsquo dv and divide up the range of possible voltages into small lsquobinsrsquo of this size We then count up how often the measured voltage was in each bin divide those counts by the total number of measurements and plot a histogram
bull We can now use this plot to indicate the likelihood or probability that any future measurement of the voltage will give a result in any particular small range
bull NYQUIST EQUATION
bull ltV2gt = 4kTRf
For frequencies below a few gigahertz Equation 1 gives the relationship between the- ltV2gt the measured mean-squared voltage - (T) absolute temperature of the resistor - ( R) its resistance - f is the bandwidth in hertz over which the noise is measured For a resistor of 1kΩ at room temperature and a 10 kHz bandwidth the RMS noise voltage is 400 nV or 04 microvolts - kB is Boltzmanrsquos constant (138 x 10-23- JoulesKelvin)
POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONSbull The frequency content of the random fluctuations are characterized by the power spectral density (PSD)bull PSD = power per unit frequencybull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoisebull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1
- f2 ) where(f1 - f2) is the bandwidth of the measurement systembullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
bull At any particular instant there may be more electrons near one end of the box than the other
bull If we note the meter reading at regular intervals (eg every second) for a long period we can plot a histogram of the results
bull we choose a lsquobin widthrsquo dv and divide up the range of possible voltages into small lsquobinsrsquo of this size We then count up how often the measured voltage was in each bin divide those counts by the total number of measurements and plot a histogram
bull We can now use this plot to indicate the likelihood or probability that any future measurement of the voltage will give a result in any particular small range
bull NYQUIST EQUATION
bull ltV2gt = 4kTRf
For frequencies below a few gigahertz Equation 1 gives the relationship between the- ltV2gt the measured mean-squared voltage - (T) absolute temperature of the resistor - ( R) its resistance - f is the bandwidth in hertz over which the noise is measured For a resistor of 1kΩ at room temperature and a 10 kHz bandwidth the RMS noise voltage is 400 nV or 04 microvolts - kB is Boltzmanrsquos constant (138 x 10-23- JoulesKelvin)
POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONSbull The frequency content of the random fluctuations are characterized by the power spectral density (PSD)bull PSD = power per unit frequencybull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoisebull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1
- f2 ) where(f1 - f2) is the bandwidth of the measurement systembullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
bull If we note the meter reading at regular intervals (eg every second) for a long period we can plot a histogram of the results
bull we choose a lsquobin widthrsquo dv and divide up the range of possible voltages into small lsquobinsrsquo of this size We then count up how often the measured voltage was in each bin divide those counts by the total number of measurements and plot a histogram
bull We can now use this plot to indicate the likelihood or probability that any future measurement of the voltage will give a result in any particular small range
bull NYQUIST EQUATION
bull ltV2gt = 4kTRf
For frequencies below a few gigahertz Equation 1 gives the relationship between the- ltV2gt the measured mean-squared voltage - (T) absolute temperature of the resistor - ( R) its resistance - f is the bandwidth in hertz over which the noise is measured For a resistor of 1kΩ at room temperature and a 10 kHz bandwidth the RMS noise voltage is 400 nV or 04 microvolts - kB is Boltzmanrsquos constant (138 x 10-23- JoulesKelvin)
POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONSbull The frequency content of the random fluctuations are characterized by the power spectral density (PSD)bull PSD = power per unit frequencybull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoisebull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1
- f2 ) where(f1 - f2) is the bandwidth of the measurement systembullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
bull We can now use this plot to indicate the likelihood or probability that any future measurement of the voltage will give a result in any particular small range
bull NYQUIST EQUATION
bull ltV2gt = 4kTRf
For frequencies below a few gigahertz Equation 1 gives the relationship between the- ltV2gt the measured mean-squared voltage - (T) absolute temperature of the resistor - ( R) its resistance - f is the bandwidth in hertz over which the noise is measured For a resistor of 1kΩ at room temperature and a 10 kHz bandwidth the RMS noise voltage is 400 nV or 04 microvolts - kB is Boltzmanrsquos constant (138 x 10-23- JoulesKelvin)
POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONSbull The frequency content of the random fluctuations are characterized by the power spectral density (PSD)bull PSD = power per unit frequencybull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoisebull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1
- f2 ) where(f1 - f2) is the bandwidth of the measurement systembullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
bull NYQUIST EQUATION
bull ltV2gt = 4kTRf
For frequencies below a few gigahertz Equation 1 gives the relationship between the- ltV2gt the measured mean-squared voltage - (T) absolute temperature of the resistor - ( R) its resistance - f is the bandwidth in hertz over which the noise is measured For a resistor of 1kΩ at room temperature and a 10 kHz bandwidth the RMS noise voltage is 400 nV or 04 microvolts - kB is Boltzmanrsquos constant (138 x 10-23- JoulesKelvin)
POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONSbull The frequency content of the random fluctuations are characterized by the power spectral density (PSD)bull PSD = power per unit frequencybull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoisebull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1
- f2 ) where(f1 - f2) is the bandwidth of the measurement systembullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
For frequencies below a few gigahertz Equation 1 gives the relationship between the- ltV2gt the measured mean-squared voltage - (T) absolute temperature of the resistor - ( R) its resistance - f is the bandwidth in hertz over which the noise is measured For a resistor of 1kΩ at room temperature and a 10 kHz bandwidth the RMS noise voltage is 400 nV or 04 microvolts - kB is Boltzmanrsquos constant (138 x 10-23- JoulesKelvin)
POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONSbull The frequency content of the random fluctuations are characterized by the power spectral density (PSD)bull PSD = power per unit frequencybull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoisebull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1
- f2 ) where(f1 - f2) is the bandwidth of the measurement systembullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONSbull The frequency content of the random fluctuations are characterized by the power spectral density (PSD)bull PSD = power per unit frequencybull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoisebull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1
- f2 ) where(f1 - f2) is the bandwidth of the measurement systembullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
Thermal Noise for Capacitancesbull Johnson noise in an RC circuit can be
expressed more simply by using the capacitance value rather than the resistance and bandwidth values The rms voltage noise on a capacitance C is independent of the resistor value since bandwidth varies reciprocally with resistance in an RC circuit
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
Shot Noise
bull Shot Noise occurs whenever any phenomenon can be
considered as a series of independent events occuring at random This occurs for carriers falling through a potential in one direction only This is a non-equilibrium process and
bull requires DC current flow First seen in vacuum tubes The spectrum is white and has a Gaussian Amplitude distribution
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
Why
bull Arises because electrons are quanta of charge and flow of charge across a junction is therefore a multiple quanta event and has to be dealt with using statistics
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
Flicker or 1f Noise
bull Inversely proportional to frequencybull Cause not well understoodbull Recognized by frequency dependencebull Becomes significant in signals lt100 Hzbull Worst for 0 Hz or DC driftbull Better in wire-wound or metallic film resistors
worse in standard carbon resistors So can be improved by using different electronic components in your circuit
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
Where1 Current in Carbon Composition resistors2 Current in Thin Metal Films (in the past not today)3 Current in Ionic Solutions4 All Solid-State components but especially Si MOSFET
GaAs5 Body Sway6 The Earthrsquos wobble on its axis7 Magnitude of Ocean waves8 Magnitude of Earthquakes9 Magnitude of Thunder Storms10 Magnitude of Tornados11 Magnitude of Hurricanes12 Classical and Jazz Music13 Economic data
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
Environmental Noise
bull Every wire in your instrument can act like an antenna to pick up electromagnetic energy and convert it into an electrical signal inside your instrument
bull There are lots of things in the environment that are putting out Electromagnetic signals
bull There are two region that are relatively noise free 3Hz to 60Hz and 1 kHz to 500 kHz
bull Will often design instruments around these frequencies to take advantage to this low environmental noise
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
Hardware Solutions
bull Grounding and Shielding
bull Difference and Instrumentation Amplifiers
bull Analog Filtering
bull Modulation
bull Signal Chopping Chopping amplifiers
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
bull Noise from environment can often be dramatically reduced by shielding grounding and minimizing wire lengths Shielding - surrounding a circuit or the wires in the circuit with a conducting material then attaching that to ground
bull Environmental EM radiation canrsquot penetrate the conductor where it gets absorbed
bull Arranging optimum shielding is something of an art something of hit and miss
bull Very important in high resistance transducers (like glass electrodes or pH electrodes Here even tiny noise get dramatically amplified
bull Wiring ndashavoid loops to reduce parasitic inductance
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
bull To amplify signal but not noise instruments typically use a difference amplifier for first stage of amplification If this isnrsquot enough a circuit called an instrumentation amplifier is used
bull With these kinds of electronics can amplify signal 1000x and eject of noise
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
Analog Filtering
bull Most common way of improving SN is with a low-pass filter Lowbull pass means that it passes slow moving signals (low frequency) but
itbull stops signals with high frequencies the jiggling noisebull Can be done with just a resistor and a capacitor This method isbull most common used in older analog instrumentsbull 1048707 You have a switch on the consol where you change either thebull capacitor or the resistor that changes the time response of thebull instrument Does reduce high frequency noise but can also damagebull signal so you have to be careful how this is used At other times
canbull use a high pass filter to pass a high frequency signal but block a lowbull frequency driftbull 1048707 Also can use narrow band or band pass filters to let just certainbull frequencies through
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-
bull 1 J Johnson Thermal Agitation of
Electricity in Conductors Phys Rev 32
97 (1928) (the experiment)
2 H Nyquist Thermal Agitation of Electric
Charge in Conductors Phys Rev 32
110 (1928) (the theory)
- Johnson-Nyquist Thermal Noise
- Some Interesting Measurements
- Noise
- History
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- POWER SPECTRAL DENSITY OF THE RANDOM FLUCTUATIONS bull The frequency content of the random fluctuations are characterized by the power spectral density (PSD) bull PSD = power per unit frequency bull The noise spectrum of the random fluctuations is wide band or ldquowhiterdquonoise bull Therefore the PSD of the random fluctuations is constant and the power is calculated by PSD (f) (f1 - f2 ) where (f1 - f2) is the bandwidth of the measurement system bullThe mean-square of the random fluctuations can be reduced by reducing the bandwidth
- Slide 13
- In communications power is often measured in decibels relative to 1 milliwatt (dBm) assuming a 50 ohm resistance With these conventions thermal noise at room temperature can be estimated as
- Thermal Noise for Capacitances
- Slide 16
- Shot Noise
- Why
- Flicker or 1f Noise
- Where
- Environmental Noise
- Hardware Solutions
- Slide 23
- Slide 24
- Analog Filtering
- Slide 26
-