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Problem in Double balanced mixer

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nikhilsigma

nikhilsigma

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Hi everyone...

I am simulating a double balanced mixer....as shown below...

Untitled.png

I am giving 2Vrms at LO input and 1Vrms(from Capacitor voltage divider) on RF input...

And I am getting 516mV DC at output(on Oscilloscope)
but I am not able to think...why am I getting such output voltage...?? since output of the mixer should be multiplication of input signals...

Please help....
 
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Your RF and LO signals are at the same frequency, so when they mix the result will have a DC offset (depending on their relative phase). So your mixer may be working properly.
 

yup that is ok....but How much should be the DC level(Amplitude) of the DC signal...
 

It's hard to estimate precisely from just a schematic. But 516mV doesn't sound too unreasonable. Your RF port signal (1Vrms) is probably too strong though, in general you want to keep it at least 10dB below your LO power.

A better test of the simulation would be to create a separate voltage source to drive the RF port with a small amplitude (like 0.1Vrms) and a small frequency offset (1KHz). Then you should get a sine wave on the IF port, and that should allow you to calculate your conversion gain.
 
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