Meterman 37XR Manual do Utilizador descarregar pdf (Página 6)

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

) is offset with the voltage stored on capacitor CM2.

The nulling amplifier (A

) measures its own offset voltage and stores it on capacitor CM1.

In the second phase (figure b), the nulling amplifier (A

) measures the input difference voltage on A

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.

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Meterman 37XR Manual do Utilizador Página 6