True Differential Techniques.
True differential amplifiers
feature complementary inputs
(+ and –) and offer high
CMRR – as high as 10,000 to 1
or higher for many instruments.
Since the amplifier’s
ability to reject the commonmode
component depends on
the degree to which the two
channels remain balanced, its
common-mode rejection ratio
will decrease with frequency
(imbalance due to effects of
stray C, etc.) and with the
magnitude of the commonmode
signal (imbalance due
to effects of amplifier overdrive).
Use of a differential probe
pair such as the P6135A (see
Figure 5) is essential to maintain
maximum CMRR.