1. NCKU/EE S.F.Lei 1 MicroElectronics Ⅲ Exercise 8.1 (a) Assume infinite R in and zero R out. Find feedback factor. (b) If the open-loop gain A=, find R 1 /R 2 to obtain a closed-loop voltage gain of 10. (c) What is the amount of feedback in decibels? (d) If =1 V, find, and. (e) If A decreases by 20%, what is the corresponding decrease in ?

2. NCKU/EE S.F.Lei 2 MicroElectronics Ⅲ Exercise 8.1

3. NCKU/EE S.F.Lei 3 MicroElectronics Ⅲ Exercise 8.1

4. NCKU/EE S.F.Lei 4 MicroElectronics Ⅲ Exercise 8.2 Consider the noninverting op-amp circuit of EXERCISE 8.1. Let the open-loop gain A have a low-frequency value of and a uniform -6 dB/octave rolloff at high frequencies with a 3-dB frequency of 100 Hz. Find the low-frequency gain and upper 3-dB frequency of a closed-loop amplifier with and.

5. NCKU/EE S.F.Lei 5 MicroElectronics Ⅲ Exercise 8.2

6. NCKU/EE S.F.Lei 6 MicroElectronics Ⅲ Example 8.1 Fig.(a) shows an noninverting op amp, given μ=, =100kΩ, =1kΩ, =2kΩ, =1kΩ, = 1MΩ, =10kΩ. Find expressions for A,β,closed-loop gain, input resistance,and the output resistance.

7. NCKU/EE S.F.Lei 7 MicroElectronics Ⅲ Example 8.1

8. NCKU/EE S.F.Lei 8 MicroElectronics Ⅲ Example 8.1

9. NCKU/EE S.F.Lei 9 MicroElectronics Ⅲ Example 8.1

10. NCKU/EE S.F.Lei 10 MicroElectronics Ⅲ Example 8.2 In fig(a), Given,,,, Find the open-loop gain A, the feedback factor β, the closed loop gain,the voltage gain,the input resistance and the output resistance. Now, if of is 25kΩ, estimate an approximate value of.

11. NCKU/EE S.F.Lei 11 MicroElectronics Ⅲ Example 8.2

12. NCKU/EE S.F.Lei 12 MicroElectronics Ⅲ Example 8.2

13. NCKU/EE S.F.Lei 13 MicroElectronics Ⅲ Example 8.2

14. NCKU/EE S.F.Lei 14 MicroElectronics Ⅲ Example 8.2

15. NCKU/EE S.F.Lei 15 MicroElectronics Ⅲ Example 8.3 Analyze the circuit of Fig(a), use β=100, determine the small-signal voltage gain, the input resistance, and the output resistance.

16. NCKU/EE S.F.Lei 16 MicroElectronics Ⅲ Example 8.3

17. NCKU/EE S.F.Lei 17 MicroElectronics Ⅲ Example 8.3

18. NCKU/EE S.F.Lei 18 MicroElectronics Ⅲ Example 8.3

19. NCKU/EE S.F.Lei 19 MicroElectronics Ⅲ Example 8.4 Fig(a) shows a feedback circuit. Find,, and Assume the transistors to have β=100 and.

20. NCKU/EE S.F.Lei 20 MicroElectronics Ⅲ Example 8.4

21. NCKU/EE S.F.Lei 21 MicroElectronics Ⅲ Example 8.4

22. NCKU/EE S.F.Lei 22 MicroElectronics Ⅲ Example 8.4

23. NCKU/EE S.F.Lei 23 MicroElectronics Ⅲ Example 8.4

24. NCKU/EE S.F.Lei 24 MicroElectronics Ⅲ Example 8.4

25. NCKU/EE S.F.Lei 25 MicroElectronics Ⅲ Exercise 8.10 Consider a feedback amplifier for which the open-loop transfer function A(s) is given by Let be a constant independent of frequency. Find. Then, show that amplifier will be stable if and unstable if and find the value of.

26. NCKU/EE S.F.Lei 26 MicroElectronics Ⅲ Exercise 8.10

27. NCKU/EE S.F.Lei 27 MicroElectronics Ⅲ Exercise 8.11 An op amp having a signal-pole rolloff ar 100Hz and a low-frequency gain of is operated in a feedback loop with. What is the factor by which feedback shifts the pole? To what frequency? If is changed to a value that results in a closed-loop gain of +1, to what frequency does the pole shift?

28. NCKU/EE S.F.Lei 28 MicroElectronics Ⅲ Exercise 8.11

29. NCKU/EE S.F.Lei 29 MicroElectronics Ⅲ Exercise 8.12 An amplifier with low-frequency gain of100 and poles at is incorporated in a negative-feedback loop with feedback factor. For what value of do the poles of the closed-loop amplifier coincide? Corresponding Q? For value of is a maximally flat response achieve? What is the low- frequency closed-loop gain in this case?

30. NCKU/EE S.F.Lei 30 MicroElectronics Ⅲ Exercise 8.12 Corresponding Corresponding gain is

31. NCKU/EE S.F.Lei 31 MicroElectronics Ⅲ Exercise 8.13 Find the closed-loop poles as function of, and show that the root locus is that of Fig. E8.13. Also find the value of at which the amplifier becomes unstable. Consider a feedback amplifier for which the open-loop transfer function A(s) is given by

32. NCKU/EE S.F.Lei 32 MicroElectronics Ⅲ Exercise 8.13

33. NCKU/EE S.F.Lei 33 MicroElectronics Ⅲ Exercise 8.13

34. NCKU/EE S.F.Lei 34 MicroElectronics Ⅲ Exercise 8.14 Consider an op amp having a signal-pole open-loop response with Let the op amp be ideal otherwise. If this amplifier is connected in the noninverting configuration with a normal low-frequency closed-loop gain of 100, find the frequency at which. Also, find the phase margin.

35. NCKU/EE S.F.Lei 35 MicroElectronics Ⅲ Exercise 8.14

36. NCKU/EE S.F.Lei 36 MicroElectronics Ⅲ Exercise 8.17 A multipole amplifier having a first pole at 1 MHz and an open-loop gain of 100 dB is to be compensated for closed-loop gains as low as 20 dB by the introduction of a new dominant pole. At what frequency must the new pole be placed?

37. NCKU/EE S.F.Lei 37 MicroElectronics Ⅲ Exercise 8.17

38. NCKU/EE S.F.Lei 38 MicroElectronics Ⅲ Exercise 8.18 If the frequency of the second pole is 10 MHz and if it remains unchanged while Additional capacitance is introduced as mentioned, find the frequency to which the first pole must be lowered so that the resulting amplifier is stable for closed- loop gains as low as 20 dB. By what factor must the capacitance at the controlling node be increased?

39. NCKU/EE S.F.Lei 39 MicroElectronics Ⅲ Exercise 8.18 The capacitance at the controlling node must be increased by same factor as f is lowered Ans. 1000 Hz; 1000