Electronic PRINCIPLESspot.pcc.edu/~wlara/eet222/slides/20.pdf · 2016. 1. 3. · Noninverting...

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MALVINO & BATES

SEVENTH EDITION

Electronic

PRINCIPLES


Linear Op-Amp Circuits

ChapterChapter2020


Topics Covered in Chapter 20

• Inverting amplifier circuits

• Noninverting amplifier circuits

• Inverter/noninverter circuits

• Differential amplifiers

• Instrumentation amplifiers


Topics Covered in Chapter 20

(Continued)

• Summing amplifier circuits

• Current boosters

• Voltage-controlled current sources

• Automatic gain control

• Single-supply operation


Inverting amplifier circuits

• One of the most basic circuits

• Voltage gain equals the ratio of the

feedback resistance to the input

resistance

• Example circuits include: ac coupled and

adjustable bandwidth


ac coupled inverting amplifier

vout

vin

R1

Rf

RL

C1

C2

AV =-Rf

R1 Rf

R1

+1

funityf2 =

fc1 = 2ππππR1C1

1fc2 = 2ππππRLC2

1


Rf

Adjustable bandwidth

voutvin

R1

RAV

f

-Rf

R1

R1 R + Rf

R1 RB =

f2 = Bfunity


Noninverting amplifier circuits

• One of the most basic circuits

• Advantages include: stable voltage gain,

high input impedance, and low output

impedance

• An example circuit is an ac coupled

noninverting amplifier


R1

Rf

ac coupled noninverting amplifier

C3

C2

C1

vout

R2

RL

vin

fc3 = 2ππππR1C3

1

Bdc = 1


Inverter / noninverter circuit

• When an input signal drives both inputs,

inverting and noninverting amplification

result at the same time

• Total voltage gain equals voltage gain of

the inverting channel plus voltage gain of

the noninverting channel


R

JFET controlled reversible gain

voutvinR

R

0 V

VGS(off)

Low gate: AV = 1

High gate: AV = −1


R

Adjustable gain of ± 1

voutvin

R


R’

Phase shifter

vout

vin

R

R’

C

φφφφ

φ φ φ φ = -2 arctan f/fc

t


R2

Differential amplifier

voutvin

R1’

R1

R2’

vin(CM)

vin(CM)

CMRR limiting factors

are the op amp itself and

the tolerance of the resistors.

AV =-R2

R1

±2 < AV(CM) < ±4∆∆∆∆R

R∆∆∆∆R

R

Ideally:

R1 = R1’

R2 = R2’


R2

Wheatstone bridge circuit

vout

R1

R4

R3

Transducer

+V


Wheatstone bridge

• The differential output signal is small.

• The common-mode output signal is large.

• Differential amplifiers are a good match.

• Input transducers convert nonelectrical

quantities into an electrical quantity.

Examples:

� photoresistor: light to resistance

� thermistor: temperature to resistance


Instrumentation amplifiers

• Differential amplifiers optimized for dc

performance

• Large differential voltage gain

• High CMRR

• Low input offsets

• Low temperature drift

• High input impedance


R

vout

vin

R

R

R

vin(CM)

vin(CM)

±2∆∆∆∆R

RAV(CM) =AV =

2R1

RG

+1

R1

R1

RG

Instrumentation amplifier


Monolithic instrumentation

amplifiers

• Use laser-trimmed resistors for high performance.

• Resistor RG is external and is selected to set the differential gain.

• Resistor RG can be split into two devices for guard driving (bootstrapping the cable shield to the common-mode potential).


RG

2

RG

2

vout

Guard driving

Guard voltage (common-mode voltage)

Instrumentation

amplifier.


Summing amplifier circuits

• Examples include: summing on both

inputs and D/A converter

• D/A converter is used in multimeters to

measure voltages, currents, and

resistances


Summing amp with inverting

and noninverting inputs

vout

R1Rf

R2

R3

R4

v1

v2

v3

v4

R5


D/A converter

vout

R R

2R

4R

8R

v3

v2

v1

v0

vout = -(v3 + 0.5v2 + 0.25v1 + 0.125v0)

Possible combinations = 2N = 24 = 16

N = 4

vin18


Current booster

• Used when short-circuit output current

of one amp is too low

• Used on the output side of the circuit

• Typically, a transistor whose base

current is supplied by the op amp

• Output current increased by the β factor


Unidirectional current booster

R2

R1 RL

vin

+VCC

vout

741

Imax = ββββdcISC = 100(25 mA) = 2.5 A

ββββdc = 100

ISC = 25 mA


Bidirectional current booster

R2

R1

RL

vin

+VCC

vout

-VEE


Voltage controlled current sources

• Input voltage controlled current sources can be configured

• Loads can be floating or grounded

• Load currents can be unidirectional or bi-directional

• The Howland current source is a bi-directional voltage controlled current source


AGC circuit

vout

R1vin

R5

R6

R3

R4

R2

+VAGC

-VEE

As the signal level increases,

VAGC goes more positive.

As the JFET rds drops,

the input signal is attenuated.

Voltage-controlled

resistance

(rds)


Single-supply operation

• Op amps typically use dual supplies.

However some applications are better

suited to a single supply.

• Some op amps are optimized for single

supply operation.


Single-supply inverting amplifier

vout

vin

R1

R2

RL

C1

C2

R

+VCC

RC3

+VCC

2

Electronic PRINCIPLESspot.pcc.edu/~wlara/eet222/slides/20.pdf · 2016. 1. 3. · Noninverting...

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