DUAL-TONE MULTIFREQUENCY RECEIVER USING SYNCHRONOUS ADDITIONS AND SUBTRACTIONS.

A new detection algorithm for a dual-tone multifrequency (DTMF) signal called the synchronous additions and subtractions (SAS) method is described. It detects a signaling tone by sampling an input signal at four times each frequency involved in a signaling tone and accumulating these sampled values synchronously by additions and subtraction. The feature of the method makes it useful for implementing flexible receivers and various types of receivers. The simplicity of the method is demonstrated by implementation of a DTMF receiver using a conventional 8-bit microcomputer without any special hardware. Only two false detections occurred for severe noise inputs of 30 h.