# Offset of an amplifier

What exactly is offset of the amplifier? How do I measure it?

In my measure lecture, lecturer told me to measure the same voltage in right polarity and opposite polarity. It should be enough to compute offset, but I can't find how to do that.

I know the amplifier has gain $100$. And it's noninverting. Values were $138\ mV$ with right polarity and $-152\ mV$ in the opposite.

I've read, that ideal amplifier has zero Offset when input voltages are equal. So is it possible to say, that offset is the value of the amplifier, when inputs are equal? Than the offset in my case could be $\frac{|138-152|}{2}$?

If the scheme is somehow important: • What is right and opposite polarities? – jippie Mar 25 '14 at 17:45
• Does this help Op Amp Input Offset Voltage – Warren Hill Mar 25 '14 at 17:55
• I mean just changing possitive and negative electrode of the input voltage. The right is the one, when amplifier has positive output. Sorry for poor English. – user50222 Mar 25 '14 at 18:18

To find the offset voltage referred to the input, divide the output offset by the gain. In this case, -70$\mu$V.
• I computed voltages on the input of the amplifier and on the output. I thought the offset is voltage on the input, if output is $0$. That would be $70\ \mu V$. If the input is $0$, output is $-70\ \mu V$. So which one it is by definition? – user50222 Mar 26 '14 at 12:01