Unstable Demodulated PWM output

[engg]

Hello everyone,
I was doing a small project showing its modulated and demodulated output. I am getting accurate PWM output but the demodulated sinewave is unstable.I have used second order low pass filter. I am stuck up and not getting any solution.

Please help!
Thanking you in advance.

 

[(*steve*)]

Please describe "unstable"

 

[engg]

I mean that the peaks of the sinewave increases and decreases constantly......

 

[(*steve*)]

What is your carrier frequency and what is the frequency of your modulating signal?

Does the demodulated signal appear to itself be (a) amplitude modulated (or (b) are the variations apparantly random?

If A, can you estimate the frequency?

Even better, can you post images of the signals and your curcuit.