Opamp input offset voltage when saturation

I wonder, how to affect the input offset voltage of inverting amplifier when it's output in saturation?

I'm changing gain with decreasing the value of R2. When the gain is greater than 5, output in saturation. But after that point the negative input voltage of opamp also increase with gain increasing.

I cannot limit the value of R2, in this case, how to avoid increasing this offset voltage?

Beacuse I am using virtual ground property of OPAMPs. This offset undesirable for me.

• It's unclear what you are asking. With +/-5V rails and a gain > 5 and 1V input the output is of course going to saturate. There will be no more virtual ground. If that's not acceptable increase your supply voltage rails or decrease your gain, there's no free lunch. Oct 5, 2019 at 23:13
• If you only need AC gain, capacitively couple by adding a cap series with R2. The DC gain will then be 1. Oct 6, 2019 at 5:32

1 Answer

I cannot limit the value of R2, in this case, how to avoid increasing this offset voltage?

The offset voltage is intrinsic to the opamp circuit, every opamp has an offset voltage. If you want to change the offset then the way to do that is with a different opamp. You will never find an op amp that can have both both inputs be the same value, you can find different op amps with lower offsets like auto zero op amps.

The offset voltage is not contributing to your saturation problem. It is offsetting the ground voltage on the negative terminal by -22uV, even with 5x gain, you'll have 220uV contribution on the output.

The saturation is happening because you are gaining 1V by 5x . 1V x 5 is 5V and that will saturate the op amp. So you can either reduce the gain, or increase the rails if you don't want saturation.

• Output saturation is not due to input offset, that is certain. But negative input voltage in saturation can be due to saturation. I need to stay both input at ground. Negative input voltage increase with gain. This is what i asking. I cannot limit R2 which is external. Oct 6, 2019 at 6:21