SIGNAL SWITCHING CIRCUIT OPERABLE IN RESPONSE TO A VOICE SIGNAL

摘要

A signal switching circuit operable in response to a voice signal but not operable in response to an audible periodic signal or signals, in which a pair of signal convertors having different trigger levels from each other are provided to generate a first pulse train and a second pulse train in response to respective intersections of the instantaneous level of the voice signal with the different trigger levels. A switching circuit is switched to a desired state when a difference between respective number of pulses of the first pulse train and the second pulse train reaches a predetermined value.