Gain Drift of PGA/opamp

[marikundam]

Given the gain drift of an opamp in specifications of opamp:

1) What parameters of an opamp are related to this gain drift?
2) How to extract them from the gain drift spec.?

 

[FvM]

In a reasonable design, the gain of an amplifier depends on the feedback dimensioning (and it's stability), not the OP parameters.
For PGA, gain stability depends strongly on the type (not a clear question, I fear).

 

[marikundam]

Feedback resistors are properly chosen taking mismatch effects into consideration. For Ex: if Rout/Rin is the Gain,Rout is multiples of Rin in design. Stability of opamp is also taken care with proper phase margins.

In PGA: first stage is a transconductance amplifier(1/Rin) and second one is transimpedance stage and Rout being feedback resistor to this stage.

My question is if the gain drift of PGA (For Ex: Gaiin=10)is to be 0.25% then How to extract spec for transconductance and transimpedance stages.

 

[dick_freebird]

Gain drift of a standalone op amp comes from device
aging / degradation (if you're talking drift over time and not
some environmental-stability spec).

A programmable gain amp, if it's discrete steps, adds some
other sensitivities such as resistor and switch resistance /
leakage drifts.

You could go backwards from lifetest data to see what else
has tracked, but I would not put much faith in predictions,
fellow-traveler-wise, until I trusted my ability to model
the individual elements' behavior over time.

Many op amp designs depend for their gain, on at least one
node being a very high impedance. That means no leakages
that have a resistive nature to them, can appear or increase.
Open loop gain is one of the most sensitive params, to small
device leakages (as might accrue from oxide charging,
mobile ions and so on).