Voice-switched telephone set

摘要

A telephone amplifier and attenuator circuit comprising an amplifier and an attenuator inserted in the transmit channel and an attenuator inserted in the receive channel of a telephone set. The speech signals conveyed by the transmit and receive channels are detected and added together for forming a sum control signal. The transmit amplifier is controlled by the detected transmit signal and the two attenuators are controlled in opposite directions by the sum control signal. In the preferred embodiment, the amplifier and attenuators are formed respectively by a balanced modulator and by balanced modulators inserted in the loop of negative feed back amplifiers.