The TP5089 is a low threshold voltage field-implanted metal gate CMOS integrated circuit It interfaces directly to a standard telephone keypad and generates all dual tone multi-frequency pairs required in tone-dialing systems The tone synthesizers are locked to an on-chip reference oscillator using an inexpensive 3 579545 MHz crystal for high tone accuracy The crystal and an output load resistor are the only external components required for tone generation A MUTE OUT logic signal which changes state when any key is depressed is also provided