I am looking for some suggestions/guidance with setting up a pre-amplifier for electrode potentials (20mV to 100mV signal range, the band-width (BW) 10kHz to 100kHz). The excitation pair represents ac current excitation (10-20mA) and the measurements pair represents potential from remaining electrodes. The electrodes have high impedance (@1kHz) of 1 MOhm. The potential between electrode are connected to instrumentation amplifier (the gain should be between 10-100) and the output connected to RMS converter. The RMS output of each channels are connected to a DAC of dsPIC microcontroller.
For additional information, both the +IN and -IN will be multiplexed.
a) I don't know if there will be some kind of switching noise or cross-talk due to the multiplexer and if I should amplify the signals before I route them to the multiplexer to increase the SNR signal/reduce switching noise?
b) What would be the multiplexing frequency recommended for this application? How to calculate them?
c) How to reduce any capacitances at the input path