The TDA1077 - An I/sup 2/L circuit for two-tone telephone dialing

The circuit-design aspects of an integrated circuit to perform two-tone telephone dialing are described. The circuit is believed to be unique in that it combines both the crystal-controlled frequency synthesizer and the output amplifier on the same chip. Moreover, no external power supplies are required; the circuit is powered by the telephone-line current. Designed to require a minimum number of external components, the LSI chip provides an economical and accurate two-tone dialing unit. A typical application circuit for existing telephone apparatus is shown and aspects of future development are discussed.