1. Feedback Xs Xi Xo + - Xf βf
What is feedback? Taking a portion of the signal arriving at the load and feeding it back to the input.
What is negative feedback? Adding the feedback signal to the input so as to partially cancel the input signal to the amplifier.
Doesn’t this reduce the gain? Yes, this is the price we pay for using feedback.
Why use feedback? Provides a series of advantages, such as:-
1-Gain desensitivity Bandwidth extension Noise reduction
4-Improves amplifier linearity

2. Feedback Amplifier AnalysisXs Xi Xo + - Xf βf

3. General feedback structure
Open loop gain
Loop gain
sedr42021_0801.jpg
Closed-loop gain

4. Basic Types of Feedback Amplifiers
Depending upon :-
Output can be a current or a voltage
Input can be a current or a voltage
There are four types of feedback amplifiers
(Type of input) (Type of output)
(1) Series (Voltage) Shunt (Voltage)
(2) Series (Voltage) Series (Current)
(3) Shunt (Current) Shunt (Voltage)
(4) Shunt (Current) Series (Current)
Terminology used to name types of feedback amplifier:-
First term refers to nature of feedback connection at the input.
Second term refers to nature of connection at the output.

5. Feedback topologies
(1) Series (Voltage) -Shunt (Voltage)

6. Feedback topologies
(2) Series (Voltage) -Series (Current)

7. Feedback topologies
(3) Shunt (Current)-Shunt (Voltage)

8. Feedback topologies
(4) Shunt (Current)-Series (Current)

9. Summary

10. Basic Types of Feedback Amplifiers
Series - Shunt
Shunt - Series
Series - Series
Shunt - Shunt

11. Method of Feedback Amplifier Analysis
Recognize the feedback amplifier’s configuration, e.g. Series-shunt
Calculate the appropriate gain A for the amplifier, e.g. voltage gain.
This includes the loading effects of the feedback circuit (some combination of resistors) on the amplifier input and output.
Calculate the feedback factor βf
Calculate the factor βf A
Calculate the feedback amplifier’s gain with feedback Af using:-
Calculate the input and output impedance.

12. Series-Shunt Feedback Amplifier - Ideal Case
feedback amplifier voltage gain Af
input resistance Rif
output resistance Rof
Basic Amplifier
Feedback Circuit
Equivalent Circuit for Feedback Amplifier

13. Series-Shunt Feedback Amplifier - Ideal Case
Midband Gain
Input Resistance
Output Resistance
For output impedance we have to make input voltage short circuit means Vs=0 It Vt