Station interface for digital electronic telephone switching system

Abstract

A station interface for a digital electronic telephone switching system is disclosed. The station interface couples a plurality of digital telephone instruments to a digital data bus having PCM encoded signals representative of analog voice signals time-division multiplexed thereon. The station interface enables two way communication between the telephone instruments and the digital data bus and includes a frame store memory for temporarily storing digital data on the data bus and assigning the digital data to system time slots. The output of the frame store memory is selectively supplied under microprocessor control to a digital audio processor which processes the PCM encoded voice signals from the telephone stations and supplies these signals to the audio processor. The audio processor digitally processes both the selected data from the frame store memory and the data from the telephone stations forwarded by a multiplexer, in respective system time slots, under microprocessor control. The PCM encoded signals are gain modified under the control of the microprocessor by the audio processor. The microprocessor monitors accumulated values of the energy of the voice signals originating at the telephone stations and those being forwarded to the telephone stations to dynamically alter the gain levels of the voice signals. In this way, differences in gain levels between signals originating from different sources, e.g. internal telephone stations or trunk lines, can be compensated. The station interface has particular application in controlling hands-free telephone station operation.