ISO2-CMOS MT8870D/MT8870D-1 Integrated DTMF Receiver Features * * * * * * * * ISSUE 5 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 Ordering Information MT8870DE/DE-1 18 Pin Plastic DIP MT8870DS/DS-1 18 Pin SOIC MT8870DN/DN-1 20 Pin SSOP -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 PWDN March 1997 VSS VRef Bias Circuit INH VRef Buffer Q1 Chip Chip Power Bias IN + High Group Filter Dial Tone Filter IN - Digital Detection Algorithm Code Converter and Latch Q2 Zero Crossing Detectors Q3 Low Group Filter GS Q4 to all Chip Clocks OSC1 OSC2 St GT St/GT Steering Logic ESt STD TOE Figure 1 - Functional Block Diagram 4-11