Electronic devices

1. Chapter 11
Op-AmpApplications

2. Op-Amp Applications
Constant-gain multiplier
Voltage summing
Voltage buffer
Controlled sources
Instrumentation circuits
Active filters
2
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.

3. Constant-Gain Amplifier
InvertingVersion
more…
3
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.

4. Constant-Gain Amplifier
Noninverting Version
4
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.

5. Multiple-Stage Gains
The total gain (3-stages) is givenby:
A  A1A2A3
or

5
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.




A  1   
R R2 R3
Rf Rf
1 
 Rf 

6. Voltage Summing

The output is the sum
of individual signals
times the gain:
[Formula 14.3]

6
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
3 
Rf
2
 1
 Rf Rf
o V3 
V2 
R
V1 
R
R
V  

7. Voltage Buffer
Any amplifier with no gain or loss is called a unitygain
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
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.

8. Controlled Sources
Voltage-controlled voltage source
Voltage-controlled current source
Current-controlled voltage source
Current-controlled current source
8
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.

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
characteristics and
gain calculations
that depend solely
on external
resistors.
Noninverting AmplifierVersion
more…
9
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.

10. 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
characteristics and
gain calculations
that depend solely
on external
resistors.
Inverting AmplifierVersion
10
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.

11. Voltage-Controlled Current Source
The output current
is:
Io 
V1  kV1
R1
11
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.

12. Current-Controlled Voltage Source
This is simply anotherway
of applying the op-amp
operation. Whether the
input is a current
determined by Vin/R1 or as
I1:
12
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
R1
Vout 
 Rf Vin
or
Vout  I1RL

13. Current-Controlled Current Source
This circuit may appear
more complicated than
the others but it is really
the same thing.
Rin
Rf
Vout  
Vin
1 2
f
in
out
R
 
R || R
Vout  
Vin

V
 
R
 in 
V  
 Rf
R
13
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
R
R || R
o
2 
   kI
2 
1 
Vin  R1  R 2 
Io  
R
 
 1 2 
R  R
 R1  R 2
Io  Vin  
2
1
Vin
Io  

 R1 
I  I 1

14. Instrumentation Circuits
Some examples of instrumentation circuits using op-
amps:
• Display driver
• Instrumentation amplifier
14
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.

15. Display Driver
15
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.

16. Instrumentation Amplifier
For all Rs at the same value (except Rp):
o
16
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
R
V1  V2  kV1  V2 
P 
2R 



V  1

17. Active Filters
Adding capacitors to op-amp circuits provides external control ofthe
cutoff frequencies. The op-amp active filter provides controllable
cutoff frequencies and controllable gain.
• Low-pass filter
• High-pass filter
• Bandpass filter
17
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.

18. Low-Pass Filter—First-Order
2πR1C1
fOH 
1
R1
18
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
Av  1 
Rf
The upper cutoff frequency
and voltage gain are given
by:

19. Low-Pass Filter—Second-Order
The roll-off can be made steeper by adding more RCnetworks.
19
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.

20. High-Pass Filter
2πR1C1
20
Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.
fOL 
1
The cutoff frequency is determined by:

21. 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, 10/e
Robert L. Boylestad and LouisNashelsky
Copyright ©2009 by Pearson Education,Inc.
Upper Saddle River, New Jersey 07458 • All rights reserved.