I have the following circuit which is an AM demodulator (I think). RF input is between the diodes left:
Plotting the bode plots for the negative and positive input of the comparator, I get a lousy allpass for the positive input (with a small notch at 10kHz) and a multi-order lowpass for the negative input.
What is R1+C6 for? If V+ should have the unfiltered input, why not directly connect RF?
If V- should be lowpass filtered, why not choose the components such that we get actual 2nd order rolloff rather than having the poles so widely spaced (or the zero in between)
At the input of the comparator is a high frequency signal which would toggle the bits at a high rate. Now I get it that the comparator is probably too slow for that but I feel it's odd relying on parasitic elements rather than actually creating the desired behavior.
Does the circuit work for for low modulation index, i.e. when I encode bits such that 1 represents a full carrier wave and 0 represents 20% attenuated carrier wave?
- Anything else to say about this circuit? Is it well known?
I also simulate this system in MATLAB, creating a 1GHz RF signal with 10kHz baseband data, demodulating the RF signal with "rf*sign(rf)" and filtering with the two calculated filters and comparing the values. I cannot get meaningful results.