Does series resistor has impact on offset voltage, bias current?

What all are the trade off?

Can calibration help minimizing errors due to added series resistor?

Does series resistor has impact on offset voltage, bias current?

What all are the trade off?

Can calibration help minimizing errors due to added series resistor?

HI,

Thanks.

We can expect max 36V at input, planned for 7.2K ohm resistor, data acquisition through AD7699.

Seems this voltage variation is very much less than ADC resolution (7.2K * 10p = 72nV). Pls correct if I am wrong.

My understanding is that due to this added resistor we have minor impact on system noise and offset.

- Do we have any other impacts?
- Does calibration help minimizing series resistor related impacts? (I understand impact is very low but to know some addition information)

Hi,

Yes. Resistor at the input and the bias current flowing at this resistor will create a voltage at that node and will appear as an error at the output. If you have large resistor x large bias current equals large offset voltage effect, however AD8655/56 has a maximum bias current of 10 pA which is low and will allow us to use larger resistor. But we can always compute the effect of bias current and resistor and assess if the resulting value is significant to affect your requirements. One big disadvantage of having large resistor is the effect of this on the overall system noise.

How high is the overvoltage are you expecting?Could you also kindly share your application.

Regards,

Phil