This document provides lecture notes on feedback amplifiers and their types. It discusses the basic concept of feedback, classification of feedback, voltage/current shunt and series feedback, and stability of feedback amplifiers. The document describes how negative feedback affects amplifier characteristics by reducing gain, increasing input resistance and bandwidth, and decreasing noise and distortion. It also defines different types of amplifiers including voltage, current, transconductance, and transresistance amplifiers, and discusses various feedback topologies.

1. Lecture Notes on Feedback
Amplifiers and its Types
for
Open Educational Resource
On
Electronic Devices and Circuits (EC201)
by
Dr. Piyush Charan
Assistant Professor
Department of Electronics and Communication Engg.
Integral University, Lucknow

2. Contents
Basic concept of feedback
General Characteristics of negative feedback amplifiers
Classification of feedback
Voltage/Current shunt and series feedback
stability of feedback amplifiers
Multistage Amplifiers, and
Tuned Amplifier.
12/01/2020 2Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow

3. Feedback
• Feedback implies feeding back (i.e., returning back) a part of the
processed signal to the input side so as to enhance or diminish the
input signal.
• When the input signal (current or voltage) is diminished, it is
considered as negative feedback.
• When the input signal is enhanced, it is known as positive feedback.
• Negative feedback is employed in amplifying systems to achieve
certain special characteristics that are not obtainable from the basic
amplifier.
• Positive feedback is employed to produce signal generator, such as
oscillators.
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 3

4. Feedback
12/01/2020 4Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow

5. Types of Feedback
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 5

6. Feedback Amplifier
• An amplifier which involves negative feedback is known as the Feedback
amplifier
• Introducing feedback varies the performance parameters of amplifier.
• Effects of Negative Feedback:
1. Improves stability of the circuit.
2. Input and output resistance can be changed with feedback network.
3. Improves frequency response of amplifier.
4. Reduces the percentage of harmonic distortion.
5. Improves the signal to noise ratio(SNR).
6. Reduces the gain of the circuit.
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 6

7. Block Diagram of Feedback
Amplifier
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 7

8. Types of Sources
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 8

9. Amplifiers
• Based on the magnitudes of the input and output
impedances of an amplifier relative to the source
and load impedances, respectively, amplifiers can
be classified into four broad categories as:
(a) Voltage amplifier,
(b) Current amplifier,
(c) Trans-conductance amplifier, and
(d) Trans-resistance amplifier.
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 9

10. Voltage Amplifier
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 10

11. Current Amplifier
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 11

12. Transconductance Amplifier
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 12

13. Transresistance Amplifier
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 13

14. Input and Output Impedances of
Basic Amplifiers
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 14

15. Sampling Network
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 15

16. Mixer Network
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 16
Series Mixing Shunt Mixing

17. Feedback Network
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 17

18. Feedback Topologies
The four basic feedback topologies: (a) voltage-mixing voltage-sampling (series–shunt) topology; (b) current-mixing current-sampling
(shunt–series) topology; (c) voltage-mixing current-sampling (series–series) topology; (d) current-mixing voltage-sampling (shunt–shunt)
topology.
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 18

19. Examples
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 19

20. Examples
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 20

21. Effects of Negative feedback
• Reduces the transfer ratio
• Increases Input resistances
• Increases gain stability
• Increases Bandwidth
• Decreases noise and distortion
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 21

22. Reduction in Transfer Ratio
12/01/2020 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 22