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problem with output from a demodulator (multiplier)

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mpradhan1

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I am working on a project which is based on lock in amplification. Basically the main phase of the design is the phase sensitive detection where demodulation(multiplication) of two signals takes place.

For my project I have to extract a very weak signal buried in large noise. In the demodulator stage, the circuit works fine if i just multiply a simple sine wave and a square wave havin da same phase as it provides me fully rectified signal. But if I add the noise signal with the sin wave and then perform the demodulation step, the output does not turn out to be fully rectified signal.

I have tried lookin at all the specs but I cant figure out whats wrong with the procedure. Can anyone please please help me out with this ?? I will really appreaciate the help :)
 
What does the output look like with noise added? Is it the rectified sine wave with nose?
 
I am working on a project which is based on lock in amplification. Basically the main phase of the design is the phase sensitive detection where demodulation(multiplication) of two signals takes place.

For my project I have to extract a very weak signal buried in large noise. In the demodulator stage, the circuit works fine if i just multiply a simple sine wave and a square wave havin da same phase as it provides me fully rectified signal. But if I add the noise signal with the sin wave and then perform the demodulation step, the output does not turn out to be fully rectified signal.

I have tried lookin at all the specs but I cant figure out whats wrong with the procedure. Can anyone please please help me out with this ?? I will really appreaciate the help :)

If you are trying to extract signal with wide bandwidth noise, then you need to apply a band pass filter at the frequency of the signal you're interested, prior to the modulator (multiplier).
 
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What does the output look like with noise added? Is it the rectified sine wave with nose?

the output of the demodulator is more like a half rectified wave where i am supposed to be gettin a fully rectified wave ... i have tried changin the various options of the circuit but still no luck

If you are trying to extract signal with wide bandwidth noise, then you need to apply a band pass filter at the frequency of the signal you're interested, prior to the modulator (multiplier).

the noise i am generating is thru da avalanche effect of a zener diode ... so am not quite sure how to chek for the bandwidth .... and also i have tried increasin the frequency of the noise to check but still no luk .... cud u help me out please ?

thanks for the earlier reply :)
 
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