Bad Circuit Design 8 - Canceling Thermal Noise
Thermal noise canít be ďcanceledĒ since itís wideband noise. Thermal noise can be
reduced by averaging, see Fig. 8.26, and by filtering (actually, averaging is also
filtering, see the bottom of page 126 in the mixed-signal book).
A couple of comments, often a designer will focus on reducing the noise in a circuit.
Well, shorting the output of an amplifier to ground reduces the amplifierís output noise
to zero but itís bad design. Itís better to focus on increasing the signal-to-noise ratio
and reducing the input-referred noise as discussed in the book. Simply reducing the
noise in a circuit doesnít mean much by itself ;-)
Flicker noise (low frequency noise) and offset (noise at DC) can be canceled. Since
these noise signals are slow moving they can be sampled and then subtracted from the
output of a circuit, see correlated double sampling, CDS, discussion in the mixed-