chapter 11 op-amp applications - dartec.com · 2017. 11. 27. · robert l. boylestad and louis...
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Chapter 11pOp-Amp Applications
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OpOp--Amp ApplicationsAmp Applications
ConstantConstant--gain multipliergain multiplierConstantConstant gain multipliergain multiplierVoltage summingVoltage summing
Voltage bufferVoltage bufferControlled sourcesControlled sources
Instrumentation circuitsInstrumentation circuitsActive filtersActive filters
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Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
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ConstantConstant--Gain AmplifierGain Amplifier
Inverting VersionInverting Version
more…more…
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ConstantConstant--Gain AmplifierGain Amplifier
Noninverting VersionNoninverting Version
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MultipleMultiple--Stage GainsStage Gains
= AAAA 321
The total gain (3-stages) is given by:
⎟⎞
⎜⎛⎟⎞
⎜⎛⎟⎞
⎜⎛ RRR
AAAA
fff
321
or
⎟⎠⎞
⎜⎝⎛−⎟⎠⎞
⎜⎝⎛−⎟⎟⎠
⎞⎜⎜⎝
⎛+=
R3R
R2R
RR1A ff
1
f
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Voltage SummingVoltage Summing
The output is the sum of individual signals times the gain:
⎟⎟⎠
⎞⎜⎜⎝
⎛++−= 3
3
f2
2
f1
1
fo VR
RV
RR
VRR
V
[Formula 14 3]
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Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
[Formula 14.3]
66
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Voltage BufferVoltage BufferAny amplifier with no gain or loss is called a unity gain unity gain amplifieramplifier. Th d t f i it i lifiThe advantages of using a unity gain amplifier:
• Very high input impedance • Very low output impedance
Realistically these circuits
• Very low output impedance
are designed using equal resistors (R1 = Rf) to avoid problems with offset voltages.
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Controlled SourcesControlled Sources
V lV l ll d lll d lVoltageVoltage--controlled voltage sourcecontrolled voltage sourceVoltageVoltage--controlled current sourcecontrolled current sourceCurrentCurrent--controlled voltage sourcecontrolled voltage sourceCurrentCurrent controlled current sourcecontrolled current sourceCurrentCurrent--controlled current sourcecontrolled current source
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VoltageVoltage--Controlled Voltage SourceControlled Voltage Source
The output voltage is the gain times the Noninverting Amplifier VersionNoninverting Amplifier Versionis the gain times the input voltage. What makes an op-amp different from other
Noninverting Amplifier VersionNoninverting Amplifier Version
different from other amplifiers is its impedance characteristics and gain calculations that depend solely on external resistors.
more…more…
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Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
99
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VoltageVoltage--Controlled Voltage SourceControlled Voltage Source
The output voltage is the gain times the Inverting Amplifier VersionInverting Amplifier Versionis the gain times the input voltage. What makes an op-amp different from other
Inverting Amplifier VersionInverting Amplifier Version
different from other amplifiers is its impedance characteristics and gain calculations that depend solely on external resistors.
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VoltageVoltage--Controlled Current SourceControlled Current Source
The output current is:
11
1o kVR
VI ==
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1111
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CurrentCurrent--Controlled Voltage SourceControlled Voltage Source
This is simply another way of applying the op ampof applying the op-amp operation. Whether the input is a current determined by Vi /R1 or asdetermined by Vin/R1 or as I1:
in1
fout VR
RV
−=
or
L1out RIV −=
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CurrentCurrent--Controlled Current SourceControlled Current Source
This circuit may appear li d hmore complicated than
the others but it is really the same thing.
inin
fout VR
RV ⎟⎟
⎠
⎞⎜⎜⎝
⎛−=
R||RV
I21
ino −=
in
in
f
out
21
in
f
out
RV
RV
R||RV
RV
−=
−=
RRR
RV
I
RRRR
VI
21ino
21
21ino
⎟⎟⎠
⎞⎜⎜⎝
⎛ +−=
⎟⎟⎠
⎞⎜⎜⎝
⎛×+
−=
inf
kIRR
1II
RR
2
1o
21
=⎟⎟⎠
⎞⎜⎜⎝
⎛+−=
⎟⎠
⎜⎝
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Instrumentation CircuitsInstrumentation Circuits
Some examples of instrumentation circuits using op-amps:
• Display driver• Instrumentation amplifier
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Display DriverDisplay Driver
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Instrumentation AmplifierInstrumentation Amplifier
For all Rs at the same value (except R ):For all Rs at the same value (except Rp):
( ) ( )2121P
o VVkVVR2R1V −=−⎟⎟
⎠
⎞⎜⎜⎝
⎛+=
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Active FiltersActive FiltersAdding capacitors to op-amp circuits provides external control of the cutoff frequencies. The op-amp active filter provides controllable
ff f i d ll bl icutoff frequencies and controllable gain.
• Low-pass filter• High pass filter• High-pass filter• Bandpass filter
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LowLow--Pass FilterPass Filter——FirstFirst--OrderOrder
The upper cutoff frequency d lt i i
11OH CRπ2
1f =1
fv R
R1A +=
and voltage gain are given by:
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LowLow--Pass FilterPass Filter——SecondSecond--OrderOrder
The roll-off can be made steeper by adding more RC networks.
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HighHigh--Pass FilterPass Filter
1The cutoff frequency is determined by:
11OL CRπ2
1f =
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Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
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Bandpass Bandpass FilterFilter
There are two cutoff frequencies: upper andfrequencies: upper and lower. They can be calculated using the same low-pass cutoff and high-low pass cutoff and highpass cutoff frequency formulas in the appropriate sections.pp p
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