A Fully Digital DTMF Receiver

An algorithm for detection of Dual Tone Multifrequency (DTMF) tones suitable for VLSI is proposed. The algorithm is based on an approximation of the correlation. The input signal is correlated with the hardlimited versions of three sinusoids having π/3 phase difference. This requires only additions and subtractions. The algorithm is realized as a fully integrated digital DTMF receiver chip fabricated in 1-μm CMOS technology.