Linear Technology Interview Question: For an op-amp with 1kOhm outp... | Glassdoor

Interview Question

Design Engineer Interview Milpitas, CA

For an op-amp with 1kOhm output impedance and 1MHz GBP (1st

  order gain rolloff), operated as a follower and driving a capacitive load, what value of capacitance will bring the phase margin to 45 degrees?
Answer

Interview Answer

2 Answers

4

Its source follower opamp so gain is one .. First pole is at 1 MHz approximately .. Op is capacitive load so we can find capacitance value.. It's one pole system .. We can get equation for phase margin equating it to 45 degrees and calculate capacitance value.

Anonymous on Jun 1, 2014
2

You know that Source follower has a gain of nearly one. So from Gain bandwidth product we can calculate the UGBW which is fairly straight forward as the gain is one. Now, from the phase margin equation you can calculate the value of the dominant pole. Also you have been given a value of output impedance and the dominant pole is 1/RC. Now you have the answer. 👍🏻

Anonymous on May 19, 2016

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