Amplitude control in digitally controlled private telephone exchange - employs peak level threshold detector signalling when level exceeded

摘要

A private automatic telephone exchange operates using pulse code modulation digital techniques and contains conversion interface circuits for connection to public telephone network operating in analogue mode. Amplitude level of analogue input is increased by signalling when a threshold level has been exceeded. In a private automatic telephone exchange speech from a subscriber is applied to an analogue to digital convertor. The analogue signals are also applied to a peak threshold level detector with feedback control signals from the convertor output. The feedback ensures that the convertor input is increased as required. Equipment at the subscriber extension receives level control signals to control the digital to analogue convertor for the receiver in response to the signals received at the exchange.