@Steve
Undersampling? You mean read the waveform for some periods and then compare maximum and minimum values that have been read to calculate the amplitude?


@Kai
Using rectifiers also crossed our mind but I think that way is not much easier than our way.

Very good point. To compensate for this problem we thought to use a calibrated phase shift between reference signals(the ones that have 90 degree phase shift relative to each other) and excitation signal but the drawback of this method is, it has to be calibrated at each frequency if they want to use other frequencies, because phase shift between generated excitation signal and applied excitation signal is somehow frequency dependent.