Here is a circuit that I have been working on for a long time now, and this is failing on certain inputs, like the AM-type sine wave, and giving almost no desired output. I have attached both the circuit and the desired result that I want to have. Please help me in this matter.

 

As far as I can see, the problem is in the response time, correct?
It seems that the circuit reacts not fast enough.
So - why not reduce the time constant of the feedback path (C1) ?
Further question: Are you sure that Q1 works in its linear operational region?
And what is the purpose of using Q1? Why not connect a suitable RC block to the gate directly?

 

hi gb22,
This is what I see using an input signal of 100Hz at 1V with steps of 100mV and 500mV, no AGC action.

I have used a different method for creating the Finp signals, modify the Voffset to suit your tests
E

 

hi gb22,
Slightly modified circuit, reduced the C1 capacitor value.
E

 

Thank you so much ericgibbs, You are a life-saver !!

 

Thank you so much ericgibbs, You are a life-saver !!

Hi gb22,
I just thought of something else to optimize your AGC circuit:

Since the diode is turned off (backward biased) when the op-amp output voltage drops (and forward-biased when this voltage goes high), the two time constants for charging and discharging the capacitor are also different.
That means: Both time constants can be separately designed by using suitable values for both resstors connected to the capacitor.