Re: Lock-in amp. Relatrogrammable band-pass/low-pass filter design.
I'm sure that is solid advice, I will follow that suggestion.
I have a few things I'd like to talk about regarding the realization of a phase sensitive detection(PSD) circuit though, you have previously recommanded a PSD made with a analog switch however while reading online I have found a few similar circuits which I don't really understand the difference of.
Firstly, I have not been able to find a lock-in amplifier(LIA) design or even a description of a LIA that uses a sine-wave as the reference which the also sine-wave excitation signal is multiplied with, which if I have understood the implication correctly would be far superior to a square-wave referenced LIA since if one uses a sine-wave reference then there would not be a lot of other frequencies along side the fundamental that is allowed to pass the PSD.
But is it even possible to multiply two sine-waves in a phase sensitive detection fashion with analog circuits, or is such a scheme only possible in the digital domain?
I am really only curious since I am pretty sure that if such a analog circuit could be designed it is well above my head, though if it is possible I will never be able to stop thinking about it until I have really really tried to make it happen(not concerning to this particular project though).
The largest confusion I have is about the following situation.
First of all, the PSD "action" is controlled by a square-wave so it has two different states or operations, the "simple switch controlled by the reference signal" ether allows the signal to pass or it breaks the signal path, which I think of as ether it multiplies the signal or it disconnects the signal path which is equal to making the signal during this state of the reference period non existent, although some designs connects the switch to ether the signal or to GND which is a much easier situation to think about becasue what would a floating node connected to the low-pass filter result in, I don't know but probably nothing.
But then there seems to be different kinds of op-amp circuits which also uses analog switches but that in both the states of the references period allows the signal to pass through to the low-pass filter, which is often described as ether multiplying the signal with +1 or -1.
But I am not able to figure out if there is a difference between those two scenarios, is there?
That is at least how I understood what i have been looking at.