A digital receiver for Dual Tone Multifrequency (DTMF) signals

A new digital receiver for Dual Tone Multifrequency (DTMF) signals is proposed in this paper. This receiver is equivalent to the optimal analog receiver. The received DTMF signal is passed through two group filters and eight very narrow bandpass tone filters. The outputs of the group filters are used to compute thresholds, while those of the tone filters are used to compute norm-sums for blocks of 80 samples. These norm-sums are compared to a theoretical expected norm-sum based on the estimated signal peak by a threshold estimation stage. The proposed receiver has a very low probability of error even when the incoming signal is severely buried in noise. It is implemented using TMS32010 assembly language and examined in real time.