In a single difference amplifier configuration, the AM-427 exhibits excellent common-mode rejection and spot nois
e voltage so low it is dominated by the resistor Johnson noise. The three-amplifier configuration shown avoids the low input-impedance characteristics of difference amplifiers. Because of the additional amplifiers used, the spectral noise voltage will increase from a typical of 3 nV/Hz to approximately 4.9 nV/Hz. The overall gain of the circuit is set at 1 000; with balanced source resistors, a CMRR of 100 dB is achieved.