A New DC Transistor Differential Amplifier

The stable amplification of low-level signals of less than 1 mv 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 operating point during aging and temperature variations. The purpose of this paper is to relate improvements in both of these respects as a result of using planar silicon transistors described by Hoerni and a compound transistor circuit. Equivalent input drifts of to have been attained over the temperature range of-70 °C to +125°C, with negligible gain variations. This circuit also offers single-ended as well as differential output capabilities.