Multifrequency (MF) Tone-Generating System for a Pulse-Code-Modulation (PCM) Digital Exchange

A digital multifrequency (MF) tone-generating system for a pulse-code-modulation (PCM) time-division multiplexed (TDM) exchange has been developed as well as the tone injection system necessary for outpulsing desired tone information in a TDM network. The tone pair is generated by reading in a predetermined sequence a memory store that contains a few binary words representing a presynthesized waveform. The necessary tone can be injected into an outgoing digital stream merely by enabling digital cross points. The system was developed and constructed for the transmission format, using currently available medium scale integration (MSI) circuits and semiconductor read-only memories (ROM). The experimental results are described. The proposed system differs conceptually from the conventional analog approach and results in a more economical system with improved stability, speed, and reliability.