SIGFRED - A LOW-POWER DTMF AND SIGNALING FREQUENCY DETECTOR

A CMOS circuit is presented containing an analog switched-capacitor processor for detection of DTMF [1] and signaling tones on a telephone subscriber line and a digital detection algorithm for postprocessing. The major issues for the design were that it should be compatible with a CMOS fabrication process for microcontrollers (mu-C) to be included as an on-chip component and that its power consumption should be as low as possible. It has been designed to work with a current of less than 0.5 mA at low supply voltages (2.5-3 V). The maximum supply voltage is limited to 6 V by the process.