electrical engineering ba (b), analog electronics, et064g 7.5 credits et065g 6 credits
DESCRIPTION
Electrical Engineering BA (B), Analog Electronics, ET064G 7.5 Credits ET065G 6 Credits. 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) - PowerPoint PPT PresentationTRANSCRIPT
1
Muhammad Amir Yousaf
Electrical Engineering BA (B), Analog Electronics,
ET064G 7.5 CreditsET065G 6 Credits
Muhammad Amir Yousaf2
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˚.
MHz
fj
kHz
fj
kHz
fj
AV
11
1
3001
1
1001
1101 5
0
Muhammad Amir Yousaf3
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M
2020
4040
6060
8080
100db100db
Muhammad Amir Yousaf4
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
Muhammad Amir Yousaf5
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M
2020
4040
6060
8080
100db100db
1M1M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
A feedback factor of -80db or Acl of 80 db can make this circuit stable.
Muhammad Amir Yousaf6
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M
2020
4040
6060
8080
100db100db
1M1M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
A feedback factor of -80db or Acl of 80 db can make this circuit stable.
(AolB)db
(Acl)db
Muhammad Amir Yousaf7
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M
2020
4040
6060
8080
100db100db
1M1M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
b) Highest bandwidth 10K
without stabilization
(Acl)db
Muhammad Amir Yousaf8
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M
2020
4040
6060
8080
100db100db
1M1M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
A feedback factor of -80db or Acl of 80 db can make this circuit stable.
Muhammad Amir Yousaf9
Lead Compensation
Muhammad Amir Yousaf10
Lead Compensation
Muhammad Amir Yousaf11
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M
2020
4040
6060
8080
100db100db
1M1M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
A Zero is placed at 10KHz to eliminate the pole at this frequency
Aol
Phase Response
Gain Response ’Lead
Compensation Circuit’
Muhammad Amir Yousaf12
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M
2020
4040
6060
8080
100db100db
1M1M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
A Zero gives +45 degree phase shift at 10KHz
Aol
Phase Response
Phase Response ’Lead
Compensation Circuit’ 00
4545
9090
Muhammad Amir Yousaf13
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M
2020
4040
6060
8080
100db100db
1M1M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
AolAdding Aol and
Lead compensation
circuit’s Gain.
Gain Response ’Lead
Compensation Circuit’
Resultant Aol after
compensation
Muhammad Amir Yousaf14
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M
00
4545
1M1M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
A Zero gives +45 degree phase shift at 10KHzAmplifier
Phase Response
Phase Response ’Lead
Compensation Circuit’
9090
Resultant phase
response
Muhammad Amir Yousaf15
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M
2020
4040
6060
8080
100db100db
1M1M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
AolAol and phase response after compensation
After compensation, we get -135degree
phase shift at 1MHz
Gain at 1MHz is 40dB. This means that the feedback factor must be atleast -40dB to get Loop Gain(AolB) = 0db a@ 1MHzSo amplifier is stable for Acl
>= 40dB
Muhammad Amir Yousaf16
But our requirement was to make it stable for 20dB amplification.
Still not achieved……
Muhammad Amir Yousaf17
Lead Compensation
Here is the solution.
This factor can be
adjusted for lower gain in
Lead compensation
ciruits
Muhammad Amir Yousaf18
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M1M1M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
Aol
Amplifier should be stabilized with 20dB
gain.
Compensation circuit Gain Response is adjusted by
selecting proper values of R1,R2-20-20
2020
4040
6060
8080
100db100db
00
Muhammad Amir Yousaf19
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M1M1M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
Aol
Resultant Gian Response
Compensation circuit Gain Response is adjusted by
selecting proper values of R1,R2-20-20
2020
4040
6060
8080
100db100db
00
Muhammad Amir Yousaf20
1010 100100 1K1K 10K10K 100K100K 1M1M 10M10M1M1M
-180-180
-135-135
-90-90
-45-45
00
-225-225
-270-270
Aol
Resultant Gian Response
Now we have 20 dB at 1MHz @ -135 degree phaseshift
-20-20
2020
4040
6060
8080
100db100db
00Feedback factor should be -20
and Acl = 20dB….Achieved