A new DC differential transistor amplifier

THE STABLE AMPLIFICATION of low level signals of less than 1 millivolt magnitude has usually been done with a carrier-type feedback amplifier employing a complex modulation-demodulation system incorporating a short-lived and bulky mechanical chopper. The much simpler all-transistor dc differential amplifier, however, has not been suitable due to drifts in gain and opiating point during aging and temperature variations. This paper will relate improvements in both, as a result of improved device characteristics obtained with the double-diffused planar silicon transistors having a passivated surface, and a compound transistor circuit.