DTMF Generator based on Interleaved Oversampling

Abstract

A circuit is described which uses one oversampling frequency synthesizer in an interleaved mode to generate dual-tone multi-frequency (DTMF) telephone dialling tones. The synthesizer is based on direct digital synthesis using phase accumulation. The Digital to analogue conversion is carried out using a first order sigma-delta (¿¿). This ¿¿ converter is also used in interleaved mode. The smoothing filter consists of a simple second order RC filter.