Posted on April 10, 2012 at 15:48To determine gain and phase shift, you need to also sample the pre-filter signal so a comparison can be made. Dual simultaneous mode using ADC1 and ADC2 can be used. Then compare peak signals for gain and zero positive or negative crossovers for phase. Since the ADC is a positive voltage device, the signals will have to be offset, so the crossover signal may, for example, be at half reference voltage.
Sampling frequency will have to be high enough to get the desired phase measurement accuracy. That accuracy can be improved by interpolating between before and after zero crossover samples.
Signal noise can be reduced by averaging multiple gain and phase measurements.
Cheers, Hal
