chapter 11 op-amp applications. copyright ©2009 by pearson education, inc. upper saddle river, new...
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Chapter 11Op-Amp Applications
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Op-Amp ApplicationsOp-Amp Applications
Constant-gain multiplierConstant-gain multiplierVoltage summingVoltage summing
Voltage bufferVoltage bufferControlled sourcesControlled sources
Instrumentation circuitsInstrumentation circuitsActive filtersActive filters
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Constant-Gain AmplifierConstant-Gain Amplifier
Inverting VersionInverting Version
more…more…
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Constant-Gain AmplifierConstant-Gain Amplifier
Noninverting VersionNoninverting Version
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Multiple-Stage GainsMultiple-Stage Gains
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R3
R
R2
R
R
R1A
AAAA
ff
1
f
321
The total gain (3-stages) is given by:
or
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Voltage SummingVoltage Summing
[Formula 14.3]
3
3
f2
2
f1
1
fo V
R
RV
R
RV
R
RV
The output is the sum of individual signals times the gain:
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Voltage BufferVoltage Buffer
Realistically these circuits are designed using equal resistors (R1 = Rf) to avoid problems with offset voltages.
Any amplifier with no gain or loss is called a unity gain unity gain amplifieramplifier. The advantages of using a unity gain amplifier:
• Very high input impedance • Very low output impedance
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Controlled SourcesControlled Sources
Voltage-controlled voltage sourceVoltage-controlled voltage source Voltage-controlled current sourceVoltage-controlled current source Current-controlled voltage sourceCurrent-controlled voltage source Current-controlled current sourceCurrent-controlled current source
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Voltage-Controlled Voltage SourceVoltage-Controlled Voltage Source
The output voltage is the gain times the input voltage. What makes an op-amp different from other amplifiers is its impedance characteristics and gain calculations that depend solely on external resistors.
Noninverting Amplifier VersionNoninverting Amplifier Version
more…more…
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Voltage-Controlled Voltage SourceVoltage-Controlled Voltage Source
The output voltage is the gain times the input voltage. What makes an op-amp different from other amplifiers is its impedance characteristics and gain calculations that depend solely on external resistors.
Inverting Amplifier VersionInverting Amplifier Version
1010
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Voltage-Controlled Current SourceVoltage-Controlled Current Source
The output current is:
11
1o kV
R
VI
1111
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Current-Controlled Voltage SourceCurrent-Controlled Voltage Source
This is simply another way of applying the op-amp operation. Whether the input is a current determined by Vin/R1 or as I1:
or
in1
fout V
R
RV
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L1out RIV
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Current-Controlled Current SourceCurrent-Controlled Current Source
This circuit may appear more complicated than the others but it is really the same thing.
in
in
f
out
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in
f
out
inin
fout
R
V
R
V
R||R
V
R
V
VR
RV
kIR
R1II
R
RR
R
VI
RR
RRVI
R||R
VI
2
1o
2
21
1
ino
21
21ino
21
ino
1313
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Instrumentation CircuitsInstrumentation Circuits
Some examples of instrumentation circuits using op-amps:
• Display driver• Instrumentation amplifier
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Display DriverDisplay Driver
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Instrumentation AmplifierInstrumentation Amplifier
For all Rs at the same value (except Rp):
2121P
o VVkVVR
2R1V
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Active FiltersActive Filters
Adding capacitors to op-amp circuits provides external control of the cutoff frequencies. The op-amp active filter provides controllable cutoff frequencies and controllable gain.
• Low-pass filter• High-pass filter• Bandpass filter
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
11OH CRπ2
1f
1
fv R
R1A
Low-Pass Filter—First-OrderLow-Pass Filter—First-Order
The upper cutoff frequency and voltage gain are given by:
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Low-Pass Filter—Second-OrderLow-Pass Filter—Second-Order
The roll-off can be made steeper by adding more RC networks.
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Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
High-Pass FilterHigh-Pass Filter
11OL CRπ2
1f
The cutoff frequency is determined by:
2020
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Bandpass Bandpass FilterFilter
There are two cutoff frequencies: upper and lower. They can be calculated using the same low-pass cutoff and high-pass cutoff frequency formulas in the appropriate sections.
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