DIGITALLY SYNTHESIZED TOUCH-TONE AUDIO SIGNAL GENERATOR

摘要

ABSTRACT OF THE DISCLOSUREA solid state signal generator for producingfrequency combinations such as used in telephone touch-tonesystems. The output of a crystal oscillator is divided toobtain binary signals proportional to the selected pairsof the seven touch-tone frequencies. These signals arescaled with selected binary output signals generated bya free-running pattern generator and representing slopesat various points on a sine wave to produce a binarysignal stream that is applied to a controlled chargedigital-to-analog conversion circuit that partiallycharges or discharges a capacitor in accordance with thebinary 1's and 0's to produce an output waveform acrossthe capacitor that corresponds to the combined pair ofselected individual tone frequency sinusoids.