11 op amp applications

1. Chapter 11
Op-Amp Applications

2. OpOp--Amp ApplicationsAmp Applications
ConstantConstant--gain multipliergain multiplier
Voltage summingVoltage summing
Voltage bufferVoltage buffer
Controlled sourcesControlled sources
Instrumentation circuitsInstrumentation circuits
Active filtersActive filters
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Active filtersActive filters
22

3. ConstantConstant--Gain AmplifierGain Amplifier
Inverting VersionInverting Version
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
more…more…
33

4. ConstantConstant--Gain AmplifierGain Amplifier
Noninverting VersionNoninverting Version
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
44

5. MultipleMultiple--Stage GainsStage Gains
= AAAA 321
The total gain (3-stages) is given by:
or
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
55






−





−





+=
R3
R
R2
R
R
R
1A ff
1
f
or

6. Voltage SummingVoltage Summing




++++++++−−−−==== fff
V
R
V
R
V
R
V
The output is the sum
of individual signals
times the gain:
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
[Formula 14.3]






++++++++−−−−==== 3
3
f
2
2
f
1
1
f
o V
R
R
V
R
R
V
R
R
V
66

7. Voltage BufferVoltage Buffer
Any amplifier with no gain or loss is called a unity gainunity gain
amplifieramplifier.
The advantages of using a unity gain amplifier:
• Very high input impedance
• Very low output impedance
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
Realistically these circuits
are designed using equal
resistors (R1 = Rf) to avoid
problems with offset
voltages.
77

8. Controlled SourcesControlled Sources
VoltageVoltage--controlled voltage sourcecontrolled voltage source
VoltageVoltage--controlled current sourcecontrolled current source
CurrentCurrent--controlled voltage sourcecontrolled voltage source
CurrentCurrent--controlled current sourcecontrolled current source
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
88

9. VoltageVoltage--Controlled Voltage SourceControlled Voltage Source
The output voltage
is the gain times the
input voltage. What
makes an op-amp
different from other
amplifiers is its
impedance
Noninverting Amplifier VersionNoninverting Amplifier Version
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
impedance
characteristics and
gain calculations
that depend solely
on external
resistors.
more…more…
99

10. VoltageVoltage--Controlled Voltage SourceControlled Voltage Source
The output voltage
is the gain times the
input voltage. What
makes an op-amp
different from other
amplifiers is its
impedance
Inverting Amplifier VersionInverting Amplifier Version
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
impedance
characteristics and
gain calculations
that depend solely
on external
resistors.
1010

11. VoltageVoltage--Controlled Current SourceControlled Current Source
The output current
is:
1
1
o kV
R
V
I ========
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
1
1
o kV
R
I ========
1111

12. CurrentCurrent--Controlled Voltage SourceControlled 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:
fR−−−−
==
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
or
in
1
f
out V
R
R
V
−−−−
====
1212
L1out RIV −=

13. CurrentCurrent--Controlled Current SourceControlled Current Source
This circuit may appear
more complicated than
the others but it is really
the same thing.
R  V
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
in
in
f
out
21
in
f
out
in
in
f
out
R
V
R
V
R||R
V
R
V
V
R
R
V
−−−−====
−−−−====






−−−−====
kI
R
R
1II
R
RR
R
V
I
RR
RR
VI
R||R
V
I
2
1
o
2
21
1
in
o
21
21
ino
21
in
o
====





++++−−−−====





 ++++
−−−−====






××××
++++
−−−−====
−−−−====
1313

14. Instrumentation CircuitsInstrumentation Circuits
Some examples of instrumentation circuits using op-
amps:
• Display driver
• Instrumentation amplifier
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
• Instrumentation amplifier
1414

15. Display DriverDisplay Driver
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
1515

16. Instrumentation AmplifierInstrumentation Amplifier
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
For all Rs at the same value (except Rp):
(((( )))) (((( ))))2121
P
o VVkVV
R
2R
1V −−−−====−−−−





++++====
1616

17. 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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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
1717

18. LowLow--Pass FilterPass Filter——FirstFirst--OrderOrder
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Electronic Devices and Circuit Theory, 10/e
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11
OH
CRπ2
1
f ====
1
f
v
R
R
1A ++++====
The upper cutoff frequency
and voltage gain are given
by:
1818

19. LowLow--Pass FilterPass Filter——SecondSecond--OrderOrder
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Electronic Devices and Circuit Theory, 10/e
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The roll-off can be made steeper by adding more RC networks.
1919

20. HighHigh--Pass FilterPass Filter
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11
OL
CRπ2
1
f ====
The cutoff frequency is determined by:
2020

21. BandpassBandpass 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
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
formulas in the
appropriate sections.
2121