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 common mode 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 common mode 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.