Digital Lock-In Amplifier

[SuperSnake428]

I have a few questions regarding lock-in amplifiers.  In my application, I do not have a reference signal because the sensor excitation is hetrodyned by an external source.  The signal of interest is the difference (or sum) of the excitation and the external source.  Both of these frequencies are however very well known.  Historically we have used the FFT of the incoming signal to extract the single tone and plot this amplitude versus time. 

My first question, would a lock-in amplifier be beneficial in this application?  It seems that the bandwidth could be reduced to much less than 1 Hz (which it currently is with the FFT) which would reduce the noise that is integrated into the signal.

Second question, is it possible to use a software PLL to generate the correct reference signal for a lock-in amplifier since I already know the frequency?

Any examples or advice would be greatly appreciated.

Thanks!

Drew

(I moved it to the hardware forum because it seemed more appropriate here than in the general labview forum).

[Aaron_W.]

Drew -

Thank you for posting on the NI Forums! I saw that another individual had posted this on the other thread:

Doug L. Bear wrote: 

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 Drew,

This definitely sounds like an application for a lock-in amplifier, which should also allow to get a bandwidth of 1 mHz or lower.  I am not quite clear on your setup but could you not just feed in your external signal as the reference signal to get the difference between your excitation and the external source?  If that is not the case, it should definitely be possible to generate a reference signal if you know the frequency. 

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I would tend to agree with Doug, this seems like and application where you could use a lock-in amplifier. Also, if you do know the frequency you should be able to generate the correct reference signal.