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Is AD8302 a lock-in amplifier?

Question asked by gr8andy on Aug 11, 2014
Latest reply on Aug 14, 2014 by gr8andy

I thought a Lock-in amplifier consist of a frequency multiplier which multiplies two incoming (logarithmic amplified to avoid clipping) signals and the frequency component (modulation frequency) that is common in both channels will show up as a DC component which varies as a cosine wave depending on the phase difference. The AC components (due to noise and twice the modulation frequency) resulting from the multiplication is filtered out. Therefore we get a DC component that is proportional to the phase difference between the 2 incoming signals. This technique supposedly can detect a signal which is small and buried in noise.

 

It seems to me that the AD8302 functions as a lock-in amplifier as it consists of logarithmic amplifiers and a frequency multiplier and a low-pass filter. Am I correct? I have 2 noisy signals (one optically delayed with respect to the other, ie a laser range finder) going into the 2 inputs of AD8302. I was hoping to get a stable phase output voltage (ie constant phase difference) as this seems like a lock-in detection to me, however the phase output voltage is unstable as it fluctuates randomly (sometimes) across the entire output range.

 

Any ideas?

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