Chapter 10 discusses operational amplifiers (op-amps), which are high gain differential amplifiers characterized by high input and low output impedance. The chapter outlines the basic configurations of op-amps, including open-loop and closed-loop setups, as well as various circuit applications such as inverting and non-inverting amplifiers, unity followers, summing amplifiers, integrators, and differentiators. Key concepts such as feedback and gain calculation using external resistors are also explained.

1. Chapter 10:
Operational Amplifiers

2. 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

3. 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
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 ‘+’

4. 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
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

5. 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
IC Product
5
V+
V-
Vo
Vin(-)
Internal circuitry of LM741.
Vin(+)

6. 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
Op-Amp
6
+

Vo
~ Vi
+

Vo
~
Vi
Non-inverting
• + terminal : Source
• – terminal : Ground
• 0o phase change
Inverting
• + terminal : Ground
• – terminal : Source
• 180o phase change

7. 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
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

8. 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
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

9. 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
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 f
v
i 1
V R
A
V R

 
1
R
R
A
R
R
1
f
v
1
f





9

10. 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
Practical Op-Amp Circuits
Inverting amplifier
Noninverting amplifier
Unity follower
Summing amplifier
Integrator
Differentiator
10

11. 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
Inverting/Noninverting Op-Amps
1
1
f
o V
R
R
V


Inverting Amplifier Noninverting Amplifier
1
1
f
o V
)
R
R
1
(
V 

11

12. 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
Unity Follower
1
o V
V 
12

13. 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
Summing Amplifier











 3
3
f
2
2
f
1
1
f
o V
R
R
V
R
R
V
R
R
V
13

14. 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
Integrator
•The output is the
integral of the input.
•This circuit is useful in
low-pass filter circuits.


 (t)dt
v
RC
1
(t)
v 1
o
14

15. 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
Differentiator
•The differentiator
takes the derivative of
the input.
•This circuit is useful
in high-pass filter
circuits.
dt
(t)
dv
RC
(t)
v 1
o 

15