Demodulator design for differentially modulated signal.

Thread Starter

Alex_Khan

Joined May 27, 2020
52
Hello,
I am demodulating differential signal using LPF based demodulator. The schematics of the entire system is attached which include diff modulator, coupling capacitors, and demodulator.
A modulated signal of 17 Mhz is demodulated. For the demodulator, I designed a 2-stage differential amplifier to amplify the diff signal then LPF is utilized to filter high frequencies, finally, the output signal is retrieved using Schmitt trigger. For LPF I used a single capacitor, the output impedance of 2-stage op-amp and capacitor constitute LPF.

Can anyone comment Why the designed 2 stage op-amp and LPF is not amplifying and filtering the modulated signal? According to my
understanding, the design op-amp parameters are adequate to demodulate the signal.

The design parameters of 2-stage op=amp are: ICMR+= 4V ICMR-=1.5V , GBW=40Mhz, Gain=68dB, Vdd=5V, C_load= 2pF.

Thanks.
 

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