A method and circuit to eliminate an offset noise, which may be produced
at or near DC (zero Hertz) in an analog, linear multiplier, is described.
An input signal is chopped (converted to another frequency) by a first
chopper, shifting a frequency of the input signal such that the
multiplier output signal is shifted away from DC. An output signal of the
multiplier is subsequently chopped again by a second chopper employing
the same chopping frequency as the first chopper. This converts a
frequency of the output signal to a desired frequency at or near DC. The
double chopping also shifts the offset noise produced by the multiplier
to a frequency, that is higher than the frequency of the output signal.
The offset noise can then be removed by a low-pass filter leaving the
output signal without the offset noise.