BELL SIGNAL GENERATING CIRCUIT

摘要

A bell signal generating circuit for a key telephone set. A dc component of a pulse signal is removed by a photo-coupler to generate a first signal. A high frequency component of the first signal is removed by a filter to generate a second signal. A differential amplifier amplifies the second signal to generate a bell signal. To the differential amplifier, a dc supply voltage based on the dc signal in synchronism with the pulse signal is applied.