The NTE1690 is a low threshold voltage, fieldimplanted, metal gate CMOS integrated circuit in a 16Lead DIP type package. This device interfaces directly to a standard telephone keypad and generates all dual tone multifrequency pairs required in tone dialing systems. The tone synthesizers are locked to an onchip reference oscillator using an inexpensive 3.579545MHz 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. Features: