I want to amplify signal coming in hundreds of channels (sensor array each producing a very low amplitude 30-200Hz signal). For every channel i care only about intensity of the signal (i don't need the actual waveform). I was thinking abut having a single amplifier tract and using electronic commutator to sweep through all the inputs. Is design like this even feasible/economical? I would appreciate any references to existing similar designs if any.
This is a standard problem in telemetry. The removal of the 60Hz interference is the major challenge, that being only one octave higher than the 30Hz you wish to preserve as signal.
I worked with a guy who developed a telemetry box (hundreds of channels) for a helicopter-design company. The sensitive sensors were wired differentially, with shielded twisted-pairs running many feet from the sensor to the centralized multiplexor-amplifier-ADC unit.
You can get 8:1 or 16:1 multiplexors. Wire 2 in parallel, to handle the balanced twisted-pairs, into a differential-input ADC.
To scan 100 sensors at 100 times per second, or 10,000 channels per second, requires 100 microsecond channel times. As the multiplexor changes to the next channel, you have to allow time for the amplifier/filter/ADC to settle accurately, to perhaps 8 bits (or 12 or whatever you need). For 12 bits, you need 9 timeconstants. Thus your analog system needs 100/9 = 11 microsecond timeconstant, such as 1MegOhm and 11 picoFarads, or 1Kohm and 11nanoFarads.