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Operational amplifier applications - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Operational_amplifier_applications

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Operational amplifier applicationsFrom Wikipedia, the free encyclopedia

This article illustrates some typical applications of solid-state integrated circuit operational amplifiers. A simplified schematic notation is used, and the reader is reminded that many details such as device selection and power supply connections are not shown.

The resistors used in these configurations are typically in the kΩ range. <1 kΩ range resistors causeexcessive current flow and possible damage to the device. >1 MΩ range resistors cause excessive thermal noise and make the circuit operation susceptible to significant errors due to bias currents.

Note: It is important to realize that the equations shown below, pertaining to each type of circuit, assume that it is an ideal op amp. Those interested in construction of any of these circuits for practical use should consult a more detailed reference. See the External links and References sections.

Contents1 Linear circuit applications

1.1 Differential amplifier1.1.1 Amplified difference1.1.2 Difference amplifier

1.2 Inverting amplifier1.3 Non-inverting amplifier1.4 Voltage follower1.5 Summing amplifier1.6 Integrator1.7 Differentiator1.8 Comparator1.9 Instrumentation amplifier1.10 Schmitt trigger1.11 Inductance gyrator1.12 Zero level detector1.13 Negative impedance converter (NIC)

2 Non-linear configurations2.1 Precision rectifier2.2 Peak detector2.3 Logarithmic output2.4 Exponential output

3 Other applications4 See also5 References6 External links

Linear circuit applications


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Differential amplifier

The circuit shown is used for finding the difference of two voltages each multiplied by some constant (determined by the resistors).

The name "differential amplifier" should not be confused with the "differentiator", also shown on this page.

Differential Zin (between the two input pins) = R1 + R2

Amplified difference

Whenever R1 = R2 and Rf = Rg,

Difference amplifier

When R1 = Rf and R2 = Rg (including previous conditions, so that R1 = R2 = Rf = Rg):

Inverting amplifier

Inverts and amplifies a voltage (multiplies by a negative constant)

Zin = Rin (because V - is a virtual ground)A third resistor, of value , added between the non-inverting input and ground, while not necessary, minimizes errors due to input bias currents.

Non-inverting amplifier

Differential amplifier

Inverting amplifier


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Amplifies a voltage (multiplies by a constant greater than 1)

(realistically, the input impedance of the op-amp itself,1 MΩ to 10 TΩ)A third resistor, of value

, added between the Vin source and the non-inverting input, while not necessary, minimizes errors due to input bias currents.

Voltage follower

Used as a buffer amplifier, to eliminate loading effects or to interface impedances (connecting a device with a high source impedance to a device with a low input impedance)

(realistically, the differential input impedance of theop-amp itself, 1 MΩ to 1 TΩ)

Summing amplifier

Sums several (weighted) voltages

When , and Rf independent

When

Output is invertedInput impedance Zn = Rn, for each input (V - is a virtual ground)

Integrator

Non-inverting amplifier

Voltage follower

Summing amplifier


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Integrates the (inverted) signal over time

(where Vin and Vout are functions of time, Vinitial is the output voltage of the integrator at time t = 0.)

Note that this can also be viewed as a type of electronic filter.

Differentiator

Differentiates the (inverted) signal over time.

The name "differentiator" should not be confused with the "differential amplifier", also shown on this page.

(where Vin and Vout are functions of time)

Note that this can also be viewed as a type of electronic filter.

Comparator

Compares two voltages and outputs one of two states depending on which is greater

Instrumentation amplifier

Combines very high input impedance, high common-mode rejection, low DC offset, and other properties used in making very accurate, low-noise measurements

Is made by adding a non-inverting buffer to each input of the differential amplifier to increase the input impedance.

Schmitt trigger

Integrating amplifier

Differentiating amplifier

Comparator

Instrumentation amplifier


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A comparator with hysteresis

Inductance gyrator

Simulates an inductor.

Zero level detector

Voltage divider reference

Zener sets reference voltage

Negative impedance converter (NIC)

Schmitt trigger

Inductance gyrator


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Creates a resistor having a negative value for any signal generator

In this case, the ratio between the input voltage and the input current (thus the input resistance) is given by:

for more information see the main article Negative impedance converter.

Non-linear configurationsPrecision rectifier

Behaves like an ideal diode for the load, which is here represented by a generic resistor RL.

This basic configuration has some limitations. For more information and to know the configuration that is actually used, see the main article.

Peak detector

When the switch is closed, the output goes to zero volts. When the switch is opened for a certain time interval, the capacitor will charge to the maximum input voltage attained during that time interval.

The charging time of the capacitor must be much shorter than the period of the highest appreciable frequency component of the input voltage.

Logarithmic output

Negative impedance converter

Super diode

Peak detector


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The relationship between the input voltage vin and the output voltage vout is given by:

where IS is the saturation current.

If the operational amplifier is considered ideal, the negative pin is virtually grounded, so the current flowing into the resistor from the source (and thus through the diode to the output, since the op-amp inputs draw no current) is:

where ID is the current through the diode. As known, the relationship between the current and the voltagefor a diode is:

This, when the voltage is greater than zero, can be approximated by:

Putting these two formulae together and considering that the output voltage Vout is the inverse of the voltage across the diode VD, the relationship is proven.

Note that this implementation does not consider temperature stability and other non-ideal effects.

Exponential output

The relationship between the input voltage vin and the output voltage vout is given by:

where IS is the saturation current.

Considering the operational amplifier ideal, then the negative pin is virtually grounded, so the current through the diode is given by:

Logarithmic configuration

Exponential configuration


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when the voltage is greater than zero, it can be approximated by:

The output voltage is given by:

Other applicationsaudio and video pre-amplifiers and buffersvoltage comparatorsdifferential amplifiersdifferentiators and integratorsfiltersprecision rectifiersvoltage regulator and current regulatoranalog-to-digital converterdigital-to-analog convertervoltage clampsoscillators and waveform generatorsSchmitt triggerGyratorComparatorActive filterAnalog computer

See alsoCurrent-feedback operational amplifierOperational transconductance amplifierFrequency compensation

ReferencesPaul Horowitz and Winfield Hill, "The Art of Electronics 2nd Ed. " Cambridge University Press, Cambridge, 1989 ISBN 0-521-37095-7Sergio Franco, "Design with Operational Amplifiers and Analog Integrated Circuits," 3rd Ed., McGraw-Hill, New York, 2002 ISBN 0-07-232084-2

External linksIntroduction to op-amp circuit stages, second order filters, single op-amp bandpass filters, and a simple intercom (http://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htm) Op Amps for Everyone (http://focus.ti.com/lit/an/slod006b/slod006b.pdf) PDFA table of standard applications (http://www.rfcafe.com/references/electrical/opamps.htm) Hyperphysics — descriptions of common applications


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(http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampvar.html) Single supply op-amp circuit collection(http://instruct1.cit.cornell.edu/courses/bionb440/datasheets/SingleSupply.pdf) PDFOp-amp circuit collection (http://www.national.com/an/AN/AN-31.pdf) PDFA Collection of Amp Applications(http://www.analog.com/UploadedFiles/Application_Notes/28080533AN106.pdf) PDF —Analog Devices Application noteBasic OpAmp Applications(http://www.ligo.caltech.edu/~vsanni/ph5/BasicOpAmpApplications.pdf) PDFHandbook of operational amplifier applications (http://focus.ti.com/lit/an/sboa092a/sboa092a.pdf) PDF — Texas Instruments Application noteLow Side Current Sensing Using Operational Amplifiers(http://focus.ti.com/analog/docs/gencontent.tsp?familyId=57&genContentId=28017) Logarithmic amplifier (http://www.play-hookey.com/analog/logarithmic_amplifier.html) Precision half-wave rectifier (http://www.play-hookey.com/analog/half-wave_rectifier.html) Precision full-wave rectifier (http://www.play-hookey.com/analog/full-wave_rectifier.html) Log/anti-log generators, cube generator, multiply/divide amp(http://www.national.com/an/AN/AN-30.pdf) PDFLogarithmically variable gain from a linear variable component(http://www.edn.com/archives/1994/030394/05di7.htm)

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Categories: Electronic amplifiers | Integrated circuits

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