1. Feedback

2. 8.4 The Series-Shunt Feedback Amplifier 8.4.1 The Ideal Situation

3. 8.4 The Series-Shunt Feedback Amplifier 8.4.1 The Ideal Situation (cont.) Series mixing

4. 8.4 The Series-Shunt Feedback Amplifier 8.4.1 The Ideal Situation (cont.) Shunt sampling

5. 8.5 The Series-Series Feedback Amplifier 8.5.1 The Ideal Situation Series mixing

6. 8.5 The Series-Series Feedback Amplifier 8.5.1 The Ideal Situation (cont.) Series sampling

7. 8.6 The Shunt-Shunt and Shunt-Series Feedback Amplifier 8.6.1 The Shunt-Shunt Configuration

8. 8.6 The Shunt-Shunt and Shunt-Series Feedback Amplifier 8.6.3 The Shunt-Series Configuration

9. 8.6 The Shunt-Shunt and Shunt-Series Feedback Amplifier 8.6.3 Summary R i  R if : Mixing Voltage (series) mixing always increases the input resistance. Current (shunt) mixing always reduces it. R o  R of : Sampling Voltage (shunt) sampling always reduces the output resistance Current (series) sampling increases it

10. 8.8 The Stability Problem 8.8.1 Transfer Function of the Feedback Amplifier Open-loop gain: A, A(s) Loop gain: A , A(s)  (s) Close-loop gain: Oscillator: =-1, zero input, infinite output

11. 8.8 The Stability Problem 8.8.2 The Nyquist Plot

12. 8.9 Effect of Feedback on the Amplifier Poles 8.9.1 Stability and Pole Location Figure 8.29 Relationship between pole location and transient response.

13. 8.9 Effect of Feedback on the Amplifier Poles 8.9.2 Poles of the feedback amplifier Simplified case

14. 8.10 Stability Study Using Bode Plots 8.10.1 Gain and Phase Margin

15. 8.10 Stability Study Using Bode Plots 8.10.2 Effect of Phase Margin on Closed-loop Response Zero margin?

16. 8.10 Stability Study Using Bode Plots 8.10.3 An Alternative Approach for Investigating Stability |AB|<1  20log|A| < 20log(1/  ) The closed-loop amplifier will be stable if the 20log(1/  ) line intersects the 20log|A| curve at a point on the -20-dB/decade segment.

17. 8.11 Frequency Compensation 8.11.1 Theory 20 40 60 80 100 10 4 10 5 10 6 10 7 10 8 1010 3 f(Hz) dB -20dB/decade -40dB/decade -60dB/decade A A’ Y Y’ Four poles Simplest Reduced the bandwidth

18. Homework: 8.37, 8.43, 8.47, Ex-8.14, 8.70, 8.76, 8.77, 8.79