User manual
An auto-zero amplifier is basically the combination of a normal op-amp (Ab), with a “nulling” op-amp
(Aa) that continually corrects for the DC offset voltage of the main amplifier.
So the device is driven by a clock (internal) that drives a two phase offset process.
In the first phase (figure a), the main amplifier (A
B
) is offset with the voltage stored on capacitor CM2.
The nulling amplifier (A
A
) measures its own offset voltage and stores it on capacitor CM1.
In the second phase (figure b), the nulling amplifier (A
A
) measures the input difference voltage on A
B
and stores this value on capacitor CM2, ready for the next cycle.
Using this process the offset voltage of the main amplifier is continually eliminated.
A side benefit of this is that it also eliminates typical op-amp 1/f noise, as the low frequency is treated
as a slowly varying input offset voltage and hence gets cancelled out.