Chapter 11 Op-Amp Applicationsdartec.com/MIC4120/CHAP11a.pdfRobert L. Boylestad and Louis Nashelsky...

Chapter 11pOp-Amp Applications

OpOp--Amp ApplicationsAmp Applications

ConstantConstant--gain multipliergain multiplierConstantConstant gain multipliergain multiplierVoltage summingVoltage summing

Voltage bufferVoltage bufferControlled sourcesControlled sources

Instrumentation circuitsInstrumentation circuitsActive filtersActive filters

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

22

ConstantConstant--Gain AmplifierGain Amplifier

Inverting VersionInverting Version

more…more…



33

ConstantConstant--Gain AmplifierGain Amplifier

Noninverting VersionNoninverting Version



44

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



55

Voltage SummingVoltage Summing

The output is the sum of individual signals times the gain:

⎟⎟⎠

⎞⎜⎜⎝

⎛++−= 3

3

f2

2

f1

1

fo V

RR

VRR

VRR

V

[Formula 14 3]



[Formula 14.3]

66

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.



77

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



88

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…



99

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.



1010

VoltageVoltage--Controlled Current SourceControlled Current Source

The output current is:

11

1o kV

RV

I ==



1111

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 V

RR

V−

=

or

L1out RIV −=



1212

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 V

RR

V ⎟⎟⎠

⎞⎜⎜⎝

⎛−=

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

=⎟⎟⎠

⎞⎜⎜⎝

⎛+−=

⎟⎠

⎜⎝



1313

Instrumentation CircuitsInstrumentation Circuits

Some examples of instrumentation circuits using op-amps:

• Display driver• Instrumentation amplifier



1414

Display DriverDisplay Driver



1515

Instrumentation AmplifierInstrumentation Amplifier

For all Rs at the same value (except R ):For all Rs at the same value (except Rp):

( ) ( )2121P

o VVkVVR2R1V −=−⎟⎟

⎠

⎞⎜⎜⎝

⎛+=



1616

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



1717

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:



1818

LowLow--Pass FilterPass Filter——SecondSecond--OrderOrder

The roll-off can be made steeper by adding more RC networks.



1919

HighHigh--Pass FilterPass Filter

1The cutoff frequency is determined by:

11OL CRπ2

1f =



2020

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



2121

Chapter 11 Op-Amp Applicationsdartec.com/MIC4120/CHAP11a.pdfRobert L. Boylestad and Louis Nashelsky...

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