AnsweredAssumed Answered

Offset Trim for AC coupled AD8429

Question asked by bnevins on Oct 8, 2015
Latest reply on Jan 23, 2017 by vicbsee

I want to use the AD8429 with the inputs AC coupled, with 100k resistors to ground at each amp input.

 

Since the offset current can be 100nA, a 10mV DC differential can exist.  To get the low noise, I need Gain of 1000, Rg= 6 ohms,

which would mean a 10V signal at the output, if the offset is not corrected.

 

If I use the Ref pin, I need to connect a +/-10V signal to it.  I also lose significant dynamic range.  Also, the source resistance must be VERY low to avoid decreasing the astronomical CMRR of the AD8429.

 

The only alternative I can see is to connect a bias network to one of the input resistors, and apply a voltage ~ 10mV

to the 100kohm resistor.

 

What other trim alternatives do I have? (if any!)offset_trim1.png

Outcomes