A transistor amplifier and discriminator with bias stabilization

Summary form only given, as follows. A low-frequency medium-gain amplifier and phase discriminator using germanium transistors is described. The circuit operates a relay from the output of an a-c resistance bridge. The output of the bridge is controlled by a thermistor temperature-sensing element. The circuit was developed for use in a continuous, non-scanning temperature monitoring system for which each monitored point required a separate bridge, amplifier and discriminator output relay. The major design problem was the requirement that the circuit be operable over a wide range of ambient temperature. Particular emphasis is placed on the solution to this problem. A method of bias-stabilization with direct coupling of the amplifier transistors is presented and a means of stabilizing the discriminator circuit is described. Design consideration and performance data are discussed.