Two of eight tone encoder

摘要: A two of eight tone encoder utilizing digital techniques to synthesize the dual tones a Touch Tone telephone operator system is provided. One sixteen switches from keyboard selects one four desired row and column tones. The circuit includes, for encoding section, counter which programmable by input signals. output drives plurality exclusive OR gates decoder resistors into resistive divider network. cooperate perform an up-down counting function. are chosen in value so that synthesized stepped sine wave generated at network, corresponding selected frequency. Similar circuitry generates waves filtered, if desired, provided as inputs summation amplifier, produces having frequency components both input.