AD8629 dual opamp giving high offset.

Hello nutshell,

We'll look into this and get back to you soon.

Best regards,
Paul

Hello nutshell ,

Please correct me if I'm wrong, the issue happens in a real/actual setup and not in simulations, right?

May I ask what are you trying to achieve on the 2nd op amp stage? What is the gain that you are trying to achieve and what is the purpose of R11 and C14? The reason why I've asked this is because from the looks of it, the 2nd op amp stage is configured in open loop. At DC, C14 will act as an open circuit and there will be no feedback path from the output to the -IN pin.

Can you try shorting R11 and C14 and then measure the offset again at R6? Shorting R11 and C14 will configure the 2nd op amp at a closed loop gain of 1.15.

If the measured offset is still high, can you try furthermore removing the relay, connect R6 to GND directly, and measure the offset again?

Thank you.

Best regards,
Paul

Sorry I wasn't clear earlier the second op-amp is configured to maintain current which is set by R6. A resistor is connected between IEXC+ & IEXC- or you can short it using multimeter in current measuring mode and it will maintain 10uA as we have a 0.1V input across 10K resistor.

The issue got resolved after I measured the voltage difference between op-amp GND and current setting resistor's i.e. R6's GND point. There were at different voltage potential due to a layout mistake, which got resolved after connecting the two GNDs externally via a wire. 

Hello nutshell,

Good to know that the issue has been resolved already.

I will now close this thread, but in case you encountered some other issues, don't hesitate to reach out again to us

Best regards,
Paul