there may be several technical solutions to avoid drift.
(Earlier chopper amplifyer modulated the DC-diffence voltage at the
inputs into AC, amplified the AC driftless and modulated this back to
I'm using the ICL7650.
This amplifier of ingenious design is "chopper stabilized OpAmp". It
uses a chopper to sense the difference voltage at the inputs of the
The OpAmp itself does not use chopping.
When the OpAmp is in a closed loop circuit, the difference should be
zero. But there is the offset voltage.
The chopper amplifier detects this offset and uses the biasing circuits
to minimize the difference.
One of the penalties occurs upon saturation of the OpAmp, caused by
overloading input signals.
In this case the chopper amplifier detects a severe difference voltage,
tries to minimize it - and produces a severe inbalance in the bias
circuit. After this event the chopper stabilized OpAmp uses some time to
find its stebility again.
You'll find further information in the data sheet.