Digital-to-analog converter for a communication system

Claim 1

A communication system for the conversion of linear pulse code modulation signals to linear delta modulation signals and then to analog signals comprising input means via which linear pulse code modulation signals are received, speed conversion means coupled to said input means including buffer register means operable to increase the frequency of the received signals, converter means for converting the signals output from said speed conversion means to two's complement format, digital filter means including register means coupled to the output of said converter means, first means for adding each word output from said converter means to the preceding word received from said register means, and second means for registering the output of said first means, further means for effectively dividing each word output from said second means by a predetermined number, means coupled to said further means to invert the sign bit to thereby convert the signals to offset binary format, a digital delta modulator including up-down counter means, said digital delta modulator being responsive to said signals in the offset binary format to output linear delta modulation signals, an analog line, integrating means coupled between the output of the digital delta modulator and the analog line to convert the delta modulated signals to analog signals, and reset means for resetting the integrating means to a zero analog level in response to detection of a zero count in the up-down counter means.