1. Chapter 9. Feedback

2. Contents Introduction The General Feedback Structure
Some Properties of Negative Feedback
The Four Basic Feedback Topologies
The Feedback Voltage Amplifier (Series—Shunt)
The Feedback Trans-conductance Amplifier (Series—Series)
The Feedback Trans-resistance Amplifier (Shunt—Shunt)
The Feedback Current Amplifier (Shunt—Series)
Summary of the Feedback Analysis Method
Determining the Loop Gain
The Stability Problem
Effect of Feedback on the Amplifier Poles
Stability Study Using Bode Plots
Frequency Compensation

3. Introduction Negative feedback의 장점
이득의 둔감화 : 증폭기 이득이 부품 값 의 변화나 온도에 둔감해짐
비선형 왜곡의 감소
잡음의 영향을 줄이기
입력 저항과 출력 저항을 제어함
증폭기의 대역폭 확대
Negative feedback의 장점은 증폭기 이득의 감소를 낳는다.

4. 1. The General Feedback Structure
β : feedback factor
Aβ : Loop gain
Af : closed-loop gain
A : Open-loop gain
1+Aβ : Amount of feedback factor

5. Example 9.1

6. Assume that the op amp has infinite input resistance and zero output resistance. Find an expression for the feedback factor β. decrease in Af.
Find the condition under which the closed-loop gain is almost entirely determined by the feedback network.
(c) If the open-loop gain 104 V/V, find R2/R1 to obtain a closed-loop gain of 10 V/V.
(d) What is the amount of feedback in decibels?
(e) If Vs =1 V, find Vo, Vf, and Vi.
(f) If A decreases by 20%, what is the corresponding decrease in Af.

7. 2. Some Properties of Negative Feedback
2.1 Gain de-sensitivity
2.2 Bandwidth extension

8. 2.3 Interference reduction
(a) Open-loop system
(b) Closed-loop system

9. Reducing power supply hum by feedback
정류기의 ripple

10. 2.4 Reduction in nonlinear distortion

11. 3. The four basic feedback topologies
(a) Voltage amplifiers (series–shunt feedback)
(b) Current amplifiers (shunt–series feedback)
(c) Trans-conductance amplifiers(series–series feedback)
(d) Trans-resistance amplifiers (shunt–shunt)

12. 3.1 Voltage Amplifiers
Examples of feedback voltage amplifiers

13. 3.2 Current amplifiers
Examples of feedback current amplifiers

14. Example 9.2

15. 3.3 Trans-conductance amplifiers
Examples of feedback trans-conductance amplifiers

16. 3.4 Trans-resistance amplifiers
Examples of feedback trans-resistance amplifiers

17. Two port network for feedback

18. Impedance parameter

19. Hybrid parameter

21. Admittance parameter