OPA2196: Vos error check

Hi even,

the input offset voltage of OPA2196 appears at output of OPA2196 multiplied by the factor "Rf / R + 1".

By the way, I would remove C354. A cap between the input pins of an OPAmp can cause stability problems. It's better to put a small cap in parallel to R351 and R352 each.

Kai

Hello Even,

The output referred voltage offset (Voso) will be primarily due to the amplified input voltage offset (Vosi) mulitplied by the noise gain of the circuit. Vosi is modeled as a voltage source in series with the non-inverting input. For this circuit the noise gain is:

Av = 1 + [R352 / (R354 || R356)] = 1 + [ 180 k / (187 || 187)] = 1926 V/V

Therefore, Vosi will be multiplied by this gain and will appear in the total Voso.

There will also be an offset contribution to Voso due to the input bias current flowing through the various input and feedback resistors.This input bias current related offset will either add to, or subtract from, the offset contibuted by the input voltage offset.

I suggest that you have a look at the TI Precision Labs session, Section 2, that covers the subject of Input Offset Voltage and Input Bias Current. That will provide insight into what makes up the total voltage offset:

Regards, Thomas

Precision Amplifiers Applications Engineering 

Here is some additional useful information:

Hi Al,

Thanks for pointing out the other E2E discussion. More good information on the voltage offset subject. Bruce is the expert on explaining op amp concepts.

Regards, Thomas
Precision Amplifiers Applications Engineering