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AD8429-AC coupled front-end

Question asked by kbm10 on May 6, 2015
Latest reply on Jun 4, 2015 by kbm10

Hi,

 

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 ?

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