What is the effect of input offset voltage in an op amp?

[jins]

Offset voltage

What is the effect of input offset voltage in an op amp?

 

[abbeyromy]

Offset voltage

@jins

While the op-amp output should be 0 V when the input is 0 V, in actual operation there is some offset voltage at the output. For example, if one connected 0 V to both op-amp inputs and then measured 26 mV(dc) at the output, this would represent 26 mV of unwanted voltage generated by the circuit and not by the input signal.

 

[LvW]

Re: Offset voltage

@jins

While the op-amp output should be 0 V when the input is 0 V, in actual operation there is some offset voltage at the output. For example, if one connected 0 V to both op-amp inputs and then measured 26 mV(dc) at the output, this would represent 26 mV of unwanted voltage generated by the circuit and not by the input signal.

26 mV at the opamp output? Nobel price for the designer!
In most cases an input offset in the uV or mV range drives the output of the opamp (without feedback!) into saturation.

 

[abbeyromy]

Offset voltage

yes the input offset voltage can range from microvolts to millivolts and can be either polarity.

@LvW
Generally the input offset would derive the op-amp into saturation. Right? so my example of 26mV is wrong cuz such a low output offset would never practically come..

So another thing that we should take into account is the gain factor. Depending upon your feedback resistors, the gain can be such that a mV of difference can lead to saturation or may not lead to saturation. Please correct me here!

Thanks for guidance!
-Hemanshu

 

[LvW]

Re: Offset voltage

.......
So another thing that we should take into account is the gain factor. Depending upon your feedback resistors, the gain can be such that a mV of difference can lead to saturation or may not lead to saturation. Please correct me here!

Yes, of course. For an opamp with feedback and a gain of - let`s say 26 - an input offest voltage of 1 mV would produce 26 mV at the output of the amplifier.
However, in this case it is the output offset of an amplifier (opamp with feedback) rather than of the opamp alone.
By the way, this offset reduction is one of the reason to have negative feedback.
The principle can be compared with the methods (emitter/source resistor) to stabilize the operating point of simple transistor stages