Electronic devices-and-circuit-theory-10th-ed-boylestad-chapter-11

Chapter 11
Op-Amp Applications

Op-Amp Applications
Constant-gain multiplier
Voltage summing
Voltage buffer
Controlled sources
Instrumentation circuits
Active filters
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
2

Constant-Gain Amplifier
Inverting Version
more……
3

Constant-Gain Amplifier
Noninverting Version
4

Multiple-Stage Gains
The total gain (3-stages) is given by:
A = A A A1 2 3
or

− 
R
A 1 f f
R
5




−  


= +
 
R3
R
R2
R
f
1

Voltage Summing



The output is the sum
of individual signals
times the gain:



R
= − f
+ f
V
+ f
V
R
V
R
V


[Formula 14.3]


  3
3
2
2
1
1
o R
R
R
6

Voltage Buffer
Any amplifier with no gain or loss is called a unity gain
amplifier.
The advantages of using a unity gain amplifier:
• Very high input impedance
• Very low output impedance
Realistically these circuits
are designed using equal
resistors (R1 = Rf) to avoid
problems with offset
voltages.
7

Controlled Sources
Voltage-controlled voltage source
Voltage-controlled current source
Current-controlled voltage source
Current-controlled current source
8

Voltage-Controlled 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 Version
characteristics and
gain calculations
that depend solely
on external
resistors.
more……
9

Voltage-Controlled 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 Version
characteristics and
gain calculations
that depend solely
on external
resistors.
10

Voltage-Controlled Current Source
The output current
is:
1
V
1
I = =
o kV
R
1
11

Current-Controlled 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:
−
Rf
=
f
R
out V
or
in
1
R
V
12
out 1 L V = −I R

Current-Controlled Current Source
This circuit may appear
more complicated than
the others but it is really
the same thing.

R

V
f
V
V
in
in
in
= −
R || R
V
I
1 2

in

= −
V
out
V
out
f
1 2
f
in
in
out
R
R
R || R
R
V
R
V
= −
 


 


= −
R +
R
1 2
 +
R R

1 2
kI
R
R
I I 1
R
R
I
R R
I V
1
2
o
2
1
o
1 2
o in
in
o

=  


 


= − +

 


 


= −
 


 


×
= −
13

Instrumentation Circuits
Some examples of instrumentation circuits using op-amps:
• Display driver
• Instrumentation amplifier
14

Display Driver
15

Instrumentation Amplifier
2R


= +
1 V − = −  
o V V k V V
For all Rs at the same value (except Rp):
( 1 2 ) ( 1 2 )
P
R


 


16

Active 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
17

Low-Pass Filter——First-Order
f
R
A = 1 +
1
OH R C 2π
1 1
f =
1
v R
The upper cutoff frequency
and voltage gain are given
by:
18

Low-Pass Filter——Second-Order
The roll-off can be made steeper by adding more RC networks.
19

High-Pass Filter
1
OL R C 2π
1 1
f =
The cutoff frequency is determined by:
20

Bandpass Filter
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
appropriate sections.
21

Electronic devices-and-circuit-theory-10th-ed-boylestad-chapter-11

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