1. Electrical Engineering BA (B), Analog Electronics, ET064G 7
Electrical Engineering BA (B), Analog Electronics, ET064G 7.5 Credits ET065G 6 Credits
Muhammad Amir Yousaf

2. Exam question An amplifier have the following open-loop gain:
 Draw a detailed asymptotic bode-diagram for the open-loop gain. Both the amplitude and phase should be clearly visualized. (2p)
What is the gain-bandwidth product for the amplifier? (1p)
What is the lowest amplification the amplifier can be used (AVmin), without any stabilization network assuming 45˚ phase margin, (ΦM). (2p)
Stabilize the amplifier with a dominant pole compensation so that it can be useful as a 20 dB amplifier with ΦM>45˚.
Muhammad Amir Yousaf

3. 100db 80 60 40 20
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M
10M

4. -45 -90 -135 -180 -225 -270 Muhammad Amir Yousaf 10 100 1K 10K 100K 1M
-45
-90
-135
-180
-225
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M
10M

5. 100db
-45 80
-90
-135 60
A feedback factor of -80db or Acl of 80 db can make this circuit stable. 40
-180 20
-225
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M 1M
10M

6. A feedback factor of -80db or Acl of 80 db can make this circuit stable.
100db
-45 80
-90
(Acl)db
-135 60 40
-180
(AolB)db 20
-225
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M 1M
10M

7. b) Highest bandwidth 10K without stabilization
b) Highest bandwidth 10K without stabilization
100db
-45 80
-90
(Acl)db
-135 60 40
-180 20
-225
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M 1M
10M

8. A feedback factor of -80db or Acl of 80 db can make this circuit stable.
100db
-45 80
-90
-135 60 40
-180 20
-225
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M 1M
10M

9. Lead Compensation
Muhammad Amir Yousaf

10. Lead Compensation
Muhammad Amir Yousaf

11. Aol A Zero is placed at 10KHz to eliminate the pole at this frequency
A Zero is placed at 10KHz to eliminate the pole at this frequency
Aol
100db
-45 80
-90
Phase Response
-135 60 40
-180
Gain Response ’Lead Compensation Circuit’ 20
-225
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M 1M
10M

12. Aol A Zero gives +45 degree phase shift at 10KHz Phase Response
A Zero gives +45 degree phase shift at 10KHz
Aol
100db
-45 80
-90
Phase Response
-135 60 40
-180 90
Phase Response ’Lead Compensation Circuit’ 45 20
-225
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M 1M
10M

13. Aol Adding Aol and Lead compensation circuit’s Gain.
Adding Aol and Lead compensation circuit’s Gain.
Aol
100db
-45 80
-90
Resultant Aol after compensation
-135 60 40
-180
Gain Response ’Lead Compensation Circuit’ 20
-225
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M 1M
10M

14. A Zero gives +45 degree phase shift at 10KHz
A Zero gives +45 degree phase shift at 10KHz
-45
Amplifier Phase Response
-90
Resultant phase response
-135
-180 90
Phase Response ’Lead Compensation Circuit’ 45
-225
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M 1M
10M

15. So amplifier is stable for Acl >= 40dB
Aol and phase response after compensation
Aol
100db
-45 80
-90
After compensation, we get -135degree phase shift at 1MHz
-135 60 40
-180
Gain at 1MHz is 40dB. This means that the feedback factor must be atleast -40dB to get Loop Gain(AolB) = 0db 1MHz 20
-225
So amplifier is stable for Acl >= 40dB
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M 1M
10M

16. But our requirement was to make it stable for 20dB amplification.
Still not achieved……
Muhammad Amir Yousaf

17. Lead Compensation
Here is the solution. This factor can be adjusted for lower gain in Lead compensation ciruits
Muhammad Amir Yousaf

18. Amplifier should be stabilized with 20dB gain.
Amplifier should be stabilized with 20dB gain. 80
-45
Aol 60
-90 40
-135
-180 20
Compensation circuit Gain Response is adjusted by selecting proper values of R1,R2
-225
-20
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M 1M
10M

19. Resultant Gian Response
100db
Resultant Gian Response 80
-45
Aol 60
-90 40
-135
-180 20
Compensation circuit Gain Response is adjusted by selecting proper values of R1,R2
-225
-20
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M 1M
10M

20. Aol Resultant Gian Response
100db
Resultant Gian Response 80
-45
Aol 60
-90 40
-135
Now we have 20 dB at -135 degree phaseshift
-180 20
Feedback factor should be -20 and Acl = 20dB….
Achieved
-225
-20
-270
Muhammad Amir Yousaf 10
100 1K
10K
100K 1M 1M
10M