1 figure 8.1 general structure of the feedback amplifier. this is a signal-flow diagram, and the...
Post on 20-Dec-2015
212 views
TRANSCRIPT
1
Figure 8.1 General structure of the feedback amplifier. This is a signal-flow diagram, and the quantities x represent either voltage or current signals.
The General Feedback Structure
FeedbackFeedback
1o
fs
x AA
x A
2
Gain Desensitivity
2(1 )f
dAdA
A
1
1f
f
dA dA
A A A
1fA
3Figure 8.2 Illustrating the application of negative feedback to improve the signal-to-noise ratio in amplifiers.
Noise Reduction
1 2 1
1 2 1 21 1o s n
A A AV V V
A A A A
4
Figure 8.3 Illustrating the application of negative feedback to reduce the nonlinear distortion in amplifiers. Curve (a) shows the amplifier transfer characteristic without feedback. Curve (b) shows the characteristic with negative feedback ( 0.01) applied.
Reduction in Nonlinear Distortion
5
Voltage-Mixing Voltage-Sampling (Series–Shunt) Feedback
voltage amplifier
6
Current-Mixing Current-Sampling (Shunt–Series) Feedback
current amplifier
let Is increase …
7
Voltage-Mixing Current-Sampling (Series–Series) Feedback
transconductance amplifier
8
Current-Mixing Voltage-Sampling (Shunt–Shunt) Feedback
transresistance amplifier
9
Figure 8.8 The series–shunt feedback amplifier: (a) ideal structure and (b) equivalent circuit.
The Series–Shunt Feedback Amplifier
10Figure 8.10 Derivation of the A circuit and circuit for the series–shunt feedback amplifier. (a) Block diagram of a practical series–shunt feedback amplifier. (b) The circuit in (a) with the feedback network represented by its h parameters.
The Practical Situation
11
Figure 8.11 Summary of the rules for finding the A circuit and for the voltage-mixing voltage-sampling case of Fig. 8.10(a).
12
Figure 8.12 Circuits for Example 8.1.
Example 8.1