Predicting AC open-loop gain for an internally compensated op-amp

  • #1
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Homework Statement


An internally compensated op amp has a DC open-loop gain of 1,000,000 (V/V) and an ac open-loop gain of 40dB at 10kHz. Provide the expected gain in dB at 1kHz...

Homework Equations


Please help, I don't know what to use for an exact answer.

The Attempt at a Solution


Beyond the break-point, the gain goes down as frequency goes up. So I just picked the value larger than 40dB (since the frequency decreased).
 
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Answers and Replies

  • #2
berkeman
Mentor
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8,005

Homework Statement


An internally compensated op amp has a DC open-loop gain of 1,000,000 (V/V) and an ac open-loop gain of 40dB at 10kHz. Provide the expected gain in dB at 1kHz...

Homework Equations


Please help, I don't know what to use for an exact answer.

The Attempt at a Solution


Beyond the break-point, the gain goes down as frequency goes up. So I just picked the value larger than 40dB (since the frequency decreased).
How many poles does an internally compensated opamp typically have, and where located? So what would you expect the rolloff to be in the 10kHz to 1kHz region?
 
  • #3
97
1
How many poles does an internally compensated opamp typically have, and where located?
What? Is there another word for poles or rolloff? I don't know what these mean.
Is my intuitive answer usually how this problem would be answered?
 
  • #4
berkeman
Mentor
57,939
8,005
What? Is there another word for poles or rolloff? I don't know what these mean.
Is my intuitive answer usually how this problem would be answered?
What class are you in? What textbook are you using? What have you found when you use the very helpful Internet to search for information on Dominant Pole Compensation for Opamps?
 
  • #5
97
1
302 Analog electronics
https://www.uwplatt.edu/files/colla... ENGINEERING TECHNICAL ELECTIVES.4.14-2_0.pdf

Microelectronics 4th edition by Neamen

Thank you for giving me a precise phase to search and learn about:
https://en.wikipedia.org/wiki/Operational_amplifier#Frequency_compensation
half-power frequency = 3dB down frequency vs the unity gain frequency...(Note to self - Lab Design project #1 III. Measurements, Amplifier gain)
http://www.ti.com/lit/an/sloa020a/sloa020a.pdf#page=19
http://web.mit.edu/klund/www/papers/ACC04_opcomp.pdf

I have to go, but I will come back and read more about this...
 
  • #6
berkeman
Mentor
57,939
8,005
ac open-loop gain of 40dB at 10kHz. Provide the expected gain in dB at 1kHz...
So I just picked the value larger than 40dB
Is my intuitive answer usually how this problem would be answered?
You are heading in the right direction, but just saying the gain is "greater" is not an answer to the question
How many poles does an internally compensated opamp typically have, and where located? So what would you expect the rolloff to be in the 10kHz to 1kHz region?
Answering those questions will give you the quantitative answer... :smile:
 

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