The Operational Amplifier

101 Pages·2014·2.41 MB·English

by  David Buchla

The Operational Amplifier
(Op-Amp)
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Electronic Devices, 9th edition
All rights reserved.
Thomas L. Floyd
Chapter Goals
• Develop understanding of linear amplification
concepts such as:
– Voltage gain, current gain, and power gain
– Gain conversion to decibel representation
– Input and output resistances
– Biasing for linear amplification
– Distortion in amplifiers
– Two-port representations of amplifiers
– Understand behavior and characteristics of ideal differential
and op amps.
– Demonstrate circuit analysis techniques for ideal op amps.
– Characterize inverting, non-inverting amplifiers.
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Electronic Devices, 9th edition
All rights reserved.
Thomas L. Floyd
Amplification
Introduction
A complex periodic signal can be represented as the sum of many
individual sine waves. We consider only one component with
amplitude V = 1 mV and frequency ω with 0 phase (signal is
s s
used as reference):

Amplifier output is sinusoidal with same frequency but different
amplitude V and phase θ:
o

© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Electronic Devices, 9th edition
All rights reserved.
Thomas L. Floyd
Amplification
Introduction (cont.)
Amplifier output power is:

Here, we desire P = 100 W with R = 8 Ω and V = 1 mV
O L s

Output power also requires output current which is:

Input current is given by

Output phase is zero because circuit is purely resistive.
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Electronic Devices, 9th edition
All rights reserved.
Thomas L. Floyd
Amplification

Voltage Gain & Current Gain
• Voltage Gain:
Magnitude and phase of voltage gain are given by
and
For our example,
• Current Gain:
Magnitude of current gain is given by
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Electronic Devices, 9th edition
All rights reserved.
Thomas L. Floyd
Amplification
Power Gain
• Power Gain:

For our example,

© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Electronic Devices, 9th edition
All rights reserved.
Thomas L. Floyd
Amplification
Expressing Gain in Decibels (dB)
The logarithmic decibel or dB scale compresses the huge numeric range of
gains encountered in real systems.
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Electronic Devices, 9th edition
All rights reserved.
Thomas L. Floyd
Amplification

Expressing Gain in dB - Example
For our example:
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Electronic Devices, 9th edition
All rights reserved.
Thomas L. Floyd
Mismatched Source and Load
Resistances
 In introductory circuit theory, the maximum power transfer
theorem is usually discussed.
 Maximum power transfer occurs when the source and load
resistances are matched (equal in value).
 In most amplifier applications, however, the opposite situation is
desired.
 A completely mismatched condition is used at both the input and
output ports of the amplifier.

© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Electronic Devices, 9th edition
All rights reserved.
Thomas L. Floyd
Mismatched Source and Load
Resistances
For the voltage amplifier shown
If R >> R and R << R , then
in s out L
In an ideal voltage amplifier,
and R = 0
out
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Electronic Devices, 9th edition
All rights reserved.
Thomas L. Floyd