Telephone station circuit using digital tone generation

摘要

A telephone instrument station circuit using a digital tone generator for generating dual tone multifrequency (DTMF) signals. The circuit employs both series and shunt muting of the receiver during the intervals occurring during the depressive and release movements of the tone generating key or button of the keyblock. The receiver is doubly muted during these intervals to prevent inductively derived spikes from causing audible clicks in the receiver. During the period of tone generation on full depression of the button, the shunt muting is released to allow the full generated tone to be sent to the line, the series muting remaining in effect.