how to measure the offset voltage of opamp? and how to minimize it?

 

http://www.analog.com/media/en/training-seminars/tutorials/MT-037.pdf

 

how to measure the offset voltage of opamp?

A couple ways would be to measure the output voltage of the opamp with both inputs at the same voltage, or apply a differential voltage to the inputs that gives a 0V output.

and how to minimize it?

It would be helpful if you gave a specific opamp or family (e.g. bipolar vs CMOS) and circuit. In general, you make the impedance on both inputs the same (for bipolar).

Some opamps have terminals for zeroing offset voltage. Those that don't use some generic circuit. From 1994 National Semiconductor Linear Applications Handbook AN-31:

 

To measure it you just configure the op amp with some inverting gain using two low value resistors (say 100Ω at the (-) input to ground and 10kΩ from the (-) input to the output, giving a gain of -100).
Ground the (+) input.
The input offset voltage is then the output voltage divided by 100.

Input offset is intrinsic to the opamp.
A few of the old opamps had an input where you could attach a pot to adjust the offset but that's not common.
You could also add a pot at the input sum in a voltage to cancel the offset at one temperature, but it won't correct if the offset varies with temperature (and it usually does).

The best solution is to buy an opamp with low offset, if it's a concern in your circuit.
There are some opamps that use an autozero technique so they have essentially zero offset.

 

A couple ways would be to measure the output voltage of the opamp with both inputs at the same voltage, or apply a differential voltage to the inputs that gives a 0V output.
It would be helpful if you gave a specific opamp or family (e.g. bipolar vs CMOS) and circuit. In general, you make the impedance on both inputs the same (for bipolar).

Some opamps have terminals for zeroing offset voltage. Those that don't use some generic circuit. From 1994 National Semiconductor Linear Applications Handbook AN-31:
View attachment 150684

I'm referring to Mosfet Pmos input Pair.

 

I'm referring to Mosfet Pmos input Pair.

Our advice is good for any type of opamp input stage.

 

A GP jig for measurements -

http://www.analog.com/en/analog-dialogue/articles/simple-op-amp-measurements.html

Regards, Dana.