Chapter 10: Operational Amplifiers - الصفحات الشخصية ...site.iugaza.edu.ps/tskaik/files/Chapter10.pdfChapter 10: Operational Amplifiers Copyright ©2009 by Pearson Education,

Chapter 10:

Operational Amplifiers

Copyright ©2009 by Pearson Education, Inc.

Upper Saddle River, New Jersey 07458 • All rights reserved.

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

Basic Op-Amp

Operational amplifier or op-amp, is a very high gain differential

amplifier with a high input impedance (typically a few meg-

Ohms) and low output impedance (less than 100 W).

Note the op-amp has two inputs and one output.

2




Basic Op-Amp

3

Symbol

• One of the input terminals (1) is called an inverting input

terminal denoted by ‘-’

• The other input terminal (2) is called a non-inverting input

terminal denoted by ‘+’




IC Product

4

+

1

2

3

4

8

7

6

5

OUTPUT A

-IN A

+IN A

V

V+

OUTPUT B

-IN B

+IN B+

Dual op-amp 1458 device




IC Product

5

V+

V-

Vo

Vin(-)

Internal circuitry of LM741.

Vin(+)




Op-Amp

6

+

Vo

~ Vi

+

Vo

~ Vi

Non-inverting

• + terminal : Source

• – terminal : Ground

• 0o phase change

Inverting

• + terminal : Ground

• – terminal : Source

• 180o phase change




Op-Amp Gain

Op-Amps have a very high gain. They can be connected open-

loop or closed-loop.

• Open-loop refers to a configuration where there is no

feedback from output back to the input. In the open-loop

configuration the gain can exceed 10,000.

• Closed-loop configuration reduces the gain. In order to

control the gain of an op-amp it must have feedback. This

feedback is a negative feedback. A negative feedback

reduces the gain and improves many characteristics of the

op-amp.

7




Inverting Op-Amp

• The signal input is applied to the inverting (–) input

• The non-inverting input (+) is grounded

• The resistor Rf is the feedback resistor. It is connected from

the output to the negative (inverting) input. This is negative

feedback.

8




Inverting Op-Amp Gain

Gain can be determined from external resistors: Rf and R1

Unity gain—voltage gain is 1

The negative sign denotes a 180 phase

shift between input and output.

o fv

i 1

V RA

V R

1R

RA

RR

1

fv

1f

9




Practical Op-Amp Circuits

Inverting amplifier

Noninverting amplifier

Unity follower

Summing amplifier

Integrator

Differentiator

10




Inverting/Noninverting Op-Amps

11

fo V

R

RV

Inverting Amplifier Noninverting Amplifier

11

fo V)

R

R1(V

11




Unity Follower

1o VV

12




Summing Amplifier

3

3

f2

2

f1

1

fo V

R

RV

R

RV

R

RV

13




Integrator

•The output is the

integral of the input.

•This circuit is useful in

low-pass filter circuits.

(t)dtvRC

1(t)v 1o

14




Differentiator

•The differentiator

takes the derivative of

the input.

•This circuit is useful

in high-pass filter

circuits.

dt

(t)dvRC(t)v 1

o

15

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Chapter 10: Operational Amplifiers - الصفحات الشخصية ...site.iugaza.edu.ps/tskaik/files/Chapter10.pdfChapter 10: Operational Amplifiers Copyright ©2009 by Pearson Education,