75T204

DESCRIPTION The 75T204 is a complete Dual-Tone Multifrequency (DTMF) receiver that detects 16 standard digits. No front-end pre-filtering is needed. The only external components required are an inexpensive 3.58-MHz television “colorburst” crystal for frequency reference and a bias resistor. An Alternate Time Base (ATB) is provided to permit operation of up to 10 75T204's from a single crystal. The 75T204 employs state-of- the-art "switched-capacitor" filter technology, resulting in approximately 40 poles of filtering, and digital circuitry on the same CMOS chip. The analog input signal is pre-processed by 60-Hz reject and band split filters and then zero-cross detected to provide AGC. Eight bandpass filters detect the individual tones. Digital processing is used to measure the tone and pause durations (continued) 75T204 5V Low-Power Subscriber DTMF Receiver FEATURES April 2000 Intended for applications with less requirements than the 75T202/75T203 14-pi...