Hello,
I have to pass a signal through one of 8 different Active Low Pass(2nd Order) filters before feed it to an 16bit ADC. signal of interest may have different frequencies, and so I need different filters for that. filters should be selected automatically(by means of a 8052 microcontroller, ofcourse). the way I was thinking about is to feed the signal(after buffering) to 8 separate filters and then connect ouput of all filters to a multiplexer and then ADC. it needs 8 OpAmps and lots of space. does anybody have a better idea?
Second question, because frequency of signal can be different, then gain of each filter should be slightly different at each frequency because I have only 8 filters and almost unlimited possibilities for signal frequency, but fortunately the exact frequency of signal is known at any moment.I need to use bessel because of its transient response. I need to calibrate ADC before sampling signal at an specified frequency(from calibrate, I mean calculating true gain of signal afer it has passed the filter and find the right coefficient for ADC output). does anybody have any suggestion for calibration procedure?

Regards.