input offset of differential amplifier

[deba_fire]

Hi All,

How should we measure the input offset of differential amplifier in lab?If I connect the inputs to their respective common modes and measure the difference between the outputs will it give me the offset voltage?Please clarify.

Thanks

 

[LvW]

The offset voltage is defined as follows: Voff is the INPUT voltage across the input terinals that is necessary to create an output of zero volts (in your case: difference between both outputs).

 

[deba_fire]

Hi LvW,

Thanks for the reply.I know the definition.But If I short the inputs to their common mode and measure the difference between the outputs(vo+ and Vo-) will this give me the offset voltage.

 

[LvW]

I don't understand why you repeat the question of your first posting.
If you know the definition you should see that your approach is NOT in agreement with the definition.
There must be a small voltage BETWEEN the input terminals that makes Vout=0.

 

[deba_fire]

Hi LvM,

I was bit confused.Now its clear.Now I have connected the OPAMP in unity feedback and measuring the difference between the outputs to know the input offset.THanks for help.

 

[leo_o2]

Your OPAMP should be differential input and single-ended output. LvW described the way for differential input and differential output opamp. By the way, you might take consideration for the loading of measurement equipment if your opamp driving capability is limited.