# Amplifier filter two poles

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#### jonnybgood

##### Full Member level 4
I have this amplifier question:
"
An amplifier has 80dB gain at low frequency; the first pole is at 1 KHz while the second pole is at 1Mhz

What is the loop gain?

Find the phase margin."

Is it possible to derive the loop gain and phase margin from the above information?

I think from the information one can consider the system as a low pass filter with a maximum dc gain of 80dB. Then there is a roll off of 20dB/ decade after the first pole and 40dB/ decade after the second one.

What is this type of amp/filter ? Is there a general circuit with a standard formula so I can simulate it and experiment with it?

What is its function ?

The questions seems to have omissions.

The terms loop gain and phase margin suggest that the amplifier (e.g. Op-Amp) is used in a feedback circuit. The feedback factor must be defined to calculate loop gain and phase margin, but it isn't mentioned.

The two-pole transfer characteristic is a typical simplified Op-Amp description and can be found in any analog electronics text book.

What is this type of amp/filter ? Is there a general circuit with a standard formula so I can simulate it and experiment with it?

What is its function ?

This is the required function:

A(s)=10000/[(1+s/w1)*(1+s/w2)] with w1=2*Pi*1E3 and w2=2*Pi*1E6

As FvM has mentioned, the phase margin and loop gain depend on the feedback.
However, in most cases the margin for unity gain operation (100% feedback) is desired.

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