Differential pair architectures are useful for differential small signal amplification where high common-mode voltage rejection (CMRR) is required. In typical differential amplifiers or fully-differential amplifiers (FDA), the tolerance of the resistors alone dominates the CMRR performance. In addition, these amplifiers cannot be configured with high input impedance because of the requirement of input resistors. When used on the front-end of an FDA, the precision-matching on the JFE2140 removes the requirement of extremely low resistor matching (< 1%) by creating a matched-input gain stage. In addition, high input impedance significantly reduces the effects of source impedance mismatch on CMRR performance, creating a differential input designed for noisy environments that are common in professional audio.

Figure 9-10 The JFE2140 as a High Input Impedance Front End for the OPA1637