I am using AD8429 (gain = 1000 )to make biopotential measurements. As I use AC coupled inputs, I add a resistor to ground as discussed in the datasheet. I also compare the measurements using a CMOS front-end commercial biopotential amplifier.
The commercial CMOS amplifier (gain = 190) has ac coupled minus the resistors as in the front-end using AD8429.
A strange observation is that, the amplitude of the input signal (output signal/gain) observed by AD8429 is smaller (by an order of magnitude 10 ) than the commercial CMOS amplifier even though the gain is higher.
Any reason why this could happen ? Is this anything to do with the input impedance of the AD8429 ?