Polarity inverter circuit for telecommunications line - feeds emitters of differential amplifier transistors from common polarity switching circuit

摘要

The invertor consists of a subscriber line circuit which contains two operational amplifiers and is controlled by the outputs of a differential amplifier. The emitters of the transistors in the differential amplifier are fed by a common polarity switching circuit; the input to the switching circuit being a logic level signal. The two differential amplifier inputs are supplied by circuits which divide the output of a voltage reference source. The reference source is also controlled by logic level signals. Current summing techniques used in the input circuit to one side of the differential amplifier ensure that temperature changes do not affect the accuracy of the inversion.