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Document related concepts
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Transcript 
Chapter 11
Amplifiers: Specifications
and
External Characteristics
1. Use various amplifier models to calculate
amplifier performance for given sources
and loads.
2. Compute amplifier efficiency.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
3. Understand the importance of input and
output
impedances of amplifiers.
4. Determine the best type of ideal amplifier
for various applications.
5. Specify the frequency-response
requirements for
various amplifier applications.
6. Understand linear and nonlinear distortion
in amplifiers.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
7. Specify the pulse-response parameters of
amplifiers.
8. Work with differential amplifiers and specify
common-mode rejection requirements.
9. Understand the various sources of dc offsets an
design balancing circuits.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
BASIC AMPLIFIER
CONCEPTS
Ideally, an amplifier produces an output
signal with identical waveshape as the
input signal, but with a larger amplitude.
vo t   Av vi t 
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Inverting versus Noninverting
Amplifiers
Inverting amplifiers have negative voltage
gain, and the output waveform is an
inverted version of the input waveform.
Noninverting
amplifiers have positive voltage gain.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Voltage-Amplifier Model
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Current Gain
io
Ai 
ii
io vo RL
Ri
Ai  
 Av
ii
vi Ri
RL
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Power Gain
Po
G
Pi
Po Vo I o
2 Ri
G

 Av Ai   Av 
Pi Vi I i
RL
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
CASCADED AMPLIFIERS
Av  Av1 Av 2
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Simplified Models for
Cascaded Amplifier Stages
First, determine the voltage gain of the first
stage
accounting for loading by the second stage.
The overall voltage gain is the product of the
gains of the separate stages.
The input impedance is that of the first stage,
and the output impedance is that of the last
ELECTRICA
L stage.
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
POWER SUPPLIES AND
EFFICIENCY
Ps  VAA I A  VBB I B
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Current-Amplifier Model
ELECTRICA
L
ENGINEERING
Principles and Applications
Aisc is the current
gain of the amplifier
with the output
short circuited.
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Transconductance-Amplifier
Model
Gmsc
iosc

vi
Connect a short circuit across the output
terminals and analyze the circuit to determine
Gmsc.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Transresistance-Amplifier
Model
Rmoc
vooc

ii
Open circuit the output terminals and
analyze the circuit to determine Rmoc.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
IMPORTANCE OF AMPLIFIER
IMPEDANCES IN VARIOUS
APPLICATIONS
Some applications call for amplifiers with high
input (or output) impedance while others call
for low input (or output) impedance.
Other applications call for amplifiers that have
specific input and/or output impedances.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
The proper classification of a given amplifier
depends on the ranges of source and load
impedances with which the amplifier is used.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
FREQUENCY RESPONSE
Vo
Av 
Vi
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Determining Complex Gain

vi t   0.1 cos2000t  30



vo t   10 cos2000t  15
Vo
1015
Av 


Vi 0.1  30

ELECTRICA
L
ENGINEERING
Principles and Applications
 10045

Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
LINEAR WAVEFORM
DISTORTION
If the gain of an amplifier has a different
magnitude for the various frequency
components
of the input signal, a form of distortion known
as amplitude distortion occurs.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Phase Distortion
If the phase shift of an amplifier is not
proportional to frequency, phase
distortion occurs.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Requirements for
Distortionless Amplification
To avoid linear waveform distortion, an
amplifier should have constant gain magnitude
and a phase
response that is linear versus frequency for
the range of frequencies contained in the input
signal.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
PULSE RESPONSE
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Rise Time
0.35
tr 
B
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Tilt
P
percentage tilt 
 100%
P
For small amounts of tilt,percentage tilt  200f LT
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
TRANSFER CHARACTERISTIC
AND NONLINEAR DISTORTION
The transfer characteristic is a plot of
instantaneous output amplitude versus
instantaneous input amplitude.
Curvature of the transfer characteristic results
in
nonlinear distortion.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Harmonic Distortion
For a sinewave input, nonlinear distortion
produces output components having
frequencies that are integer multiples of the
input frequency. v t   V cos t 
i
a
a
vo t   V0  V1 cos a t   V2 cos2 a t   V3 cos3 a t   
V2
D2 
V1
V3
D3 
V1
V4
D4 
V1
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Total Harmonic Distortion
(THD)
Total harmonic distortion is a specification
that indicates the degree of nonlinear
distortion produced by an amplifier.
D  D  D  D  D 
2
2
2
3
2
4
2
5
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
DIFFERENTIAL AMPLIFIERS
A differential amplifier has two input terminals:
an
inverting input and a noninverting input.
Ideally, a differential amplifier produces an
output that is proportional to the difference
between two input signals.
vid  vi1  vi 2
vo  Ad vid
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Common-mode Signal
vicm
1
 vi1  vi 2 
2
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Common-Mode Rejection
Ratio
vo  Ad vid  Acm vicm
CMRR  20 log
Ad
Acm
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
OFFSET VOLTAGE,
BIAS CURRENT, AND
OFFSET CURRENT
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
Real differential amplifiers suffer from
imperfections that can be modeled by
several
dc sources: two bias-current sources, an
offset current source, and an offset voltage
source. The effect of these sources is to add
a (usually undesirable) dc term to the ideal
output.
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
ELECTRICA
L
ENGINEERING
Principles and Applications
Chapter 11
Amplifiers: Specifications and External Characteristics
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