GB1014602A - Improvements relating to apparatus for converting pulse code signals into analogue form - Google Patents

Abstract

1,014,602. Selective signalling. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. April 24, 1962 [May 15, 1961], No. 17603/61. Heading G4H. In a digital-to-analogue converter using a Shannon-Rack decoder the digital signals from a number of locations are combined prior to feeding the decoder. In the embodiment described, there are seven inputs, IN1-IN7, each comprising a serial five-unit binary number, the least significant digit arriving first. The word elements are gated to current generators CG1-CG7 which give a unit current if the corresponding input is in its one state. The currents are combined and used to trigger a Shannon-Rack form of decoder which, after all seven five-unit signals have been received, gives an output dependent on the sum of the input signals. This output is stored in a " positive " store. Negative numbers are indicated by the addition of a sign bit to the inverse of the number. Each sign bit causes a signal weighted thirty-one units to be added to a " negative " store. To obtain the resultant analogue signal the contents of the stores are added. If required, the individual inputs can be weighted by weighting the generators CG and the thirty-one-unit generators.