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I have a noisy signal which is the voltage output from a photodetector circuit. I have researched about extracting signals, and found that lock-in amplifiers are one of the main approaches for the photodetector circuit.

I have a laser which is on for 5s and off for 5s. I am measuring the voltage from a photodetector circuit respective to that laser. The voltage has an amplitude of 1V and has noise. I wrote a python code for lock-in amplifier and got the below outputs.

enter image description here

But the output of the reconstructed signal is having amplitude from -0.5V to 0.5V. How can i get the output voltage correctly?

The SNR of both the input and extracted signals are below. SNR of Input Noisy Signal: -2.36 dB SNR of Extracted Output: 5.33 dB

As you can see that the SNR of the extracted is not very good. Can anyone suggest whether my approach is a correct?

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    $\begingroup$ Frankly, a lock-in amplifier (LIA) is not what I would use because it is intended to provide you an estimate of amplitude of the signal that is buried in the noise. The frequency is known in advance, because you have the reference wave form. And even early LIAs allowed for appropriate phase adjustment. So the LIA is a type of matched filter that uses the frequency and phase information optimally and gives you the amplitude estimate. Maybe looking at my LIA answer here will help a bit. $\endgroup$
    – Ed V
    Commented Aug 19, 2023 at 20:10

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