[time-nuts] EFC tracking

Chuck Harris cfharris at erols.com
Sat Jun 26 14:16:03 UTC 2010

Oz-in-DFW wrote:
> Chopping is used to cancel DC offsets in imperfect amplifiers, it adds
> no gain. If there is a DC component and you filter with a cutoff
> frequency below the chop rate, the offsets of the amplifier can be
> effectively canceled.

Chopping isn't quite that magical.  You chop the DC signal before the
first amplifier, and synchronously (usually) detect the amplified signal
after the last amplifier.

The key benefit to chopped amplifiers is the high gain stages can be
AC coupled, which eliminates any DC drifting in the high gain amplifiers
from affecting the results.

Chopping doesn't cancel any DC offsets that might exist in the input signal,
or in the input, or output, chopper mechanism.

-Chuck Harris

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