MT8870

® ISO2-CMOS MT8870D/MT8870D-1 Integrated DTMF Receiver Features Complete DTMF Receiver Low power consumption Internal gain setting amplifier Adjustable guard time Central office quality Power-down mode Inhibit mode Backward compatible with MT8870C/MT8870C-1 ISSUE 3 May1995 Ordering Information MT8870DE/DE-1 18 Pin Plastic DIP MT8870DC/DC-1 18 Pin Ceramic DIP MT8870DS/DS-1 18 Pin SOIC MT8870DN/DN-1 20 Pin SSOP MT8870DT/DT-1 20 Pin TSSOP -40 °C to +85 °C Description The MT8870D/MT8870D-1 is a complete DTMF receiver integrating both the bandsplit filter and digital decoder functions. The filter section uses switched capacitor techniques for high and low group filters; the decoder uses digital counting techniques to detect and decode all 16 DTMF tonepairs into a 4-bit code. External component count is minimized by on chip provision of a differential input amplifier, clock oscillator and latched three-state bus interface. Applications Receiver system for British Telecom (BT) or CEPT Spec (MT8870D-1) Paging systems Repeater systems/mobile radio Credit card systems Remote control Personal computers Telephone answering machine VDD VSS VRef INH PWDN Bias Circuit VRef Buffer Q1 Chip Chip Power Bias IN + IN GS Dial Tone Filter High Group Filter Zero Crossing Detectors Low Group Filter Digital Detection Algorithm Code Converter and Latch Q2 Q3 Q4 to all Chip Clocks St GT Steering Logic OSC1 OSC2 St/GT ESt STD TOE Figure 1 - Functi...