Multiple-Tone Detector with CCD Filters

An integrated-circuit multiple-tone detector is demonstrated. It is made of three transversal CCD filters with nonoverlaping bandpass characteristics for tone (i.e., sine wave signal) separation and each filter has an internally matched threshold level for reproducible tone detection. When an in-band tone exceeds the threshold level, the output for that particular filter is a square wave with the same period as the tone period. The chip was fabricated in the NMOS double layer polysilicon technology, operates on three power supplies and a master clock, measures 85 × 283 mils and dissipates only 100 mW of power. Voltage tracking, offset canceling, and area matching techniques are used in order to reduce the dependence on process or voltage supply variations.