Hi,
Can you provide some more information on the internal nulling circuit topology for this op-amp?
I have to design a circuit with automated offset compensation and wanted to see if I can make use of the Nulling pins available on this device but I have no information on the internal structure/connection.
Thanks,
Vlad
Hello Vlad,
That input nulling circuit looks like the figure below. In order to lower the offset voltage, a potentiometer is usually used to add resistance to either inverting (Vi-) or non inverting pin(Vi+) to put the output offset voltage as small as possible.
For example Vos = Vi(–) – Vi(+). If Vos is negative, then Vi(–) is smaller than Vi(+) so more resistance needs to be added to the NULL2 pin (which ties to the inverting input branch) in order to produce more voltage at this node; thus, Vos becomes less negative.
These Null pins is either connected to V-/Gnd or V+ but for AD8675, it is connected to V+. I showed the Nulling circuit for AD8675 below too.
Here are some articles about Nulling on op amps that might be of help too:
https://www.analog.com/media/en/training-seminars/tutorials/MT-037.pdf
Demystifying Auto-Zero Amplifiers-Part 1 | Analog Devices
Best Regards,
Kenneth
