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
Our ADG5204 is a newer part and is a good part with low charge injection and capacitance values. Also it is latch up proof so I would say go with this one. But note it has an Ron in the region of 160 typical. It sounds like low capacitance is a priority in your application and the amplifiers have a high input impedance.