Circuit de décodage et de codage à caractéristique logarithmique

1,150,866. Non-linear digital/analogue converters. INTERNATIONAL STANDARD ELECTRIC CORP. 18 Jan., 1968 [26 Jan., 1967], No. 2694/68. Heading G4H. A non-linear digital to analogue decoder having a logarithmic characteristic includes a register RG (Fig. 2) for the binary number to be decoded, the most significant bit of which represents its polarity, and two decoders D1, D2 for the more significant and less significant bits respectively, the outputs from decoder D1 controlling via electronic gates C11-C14, C111-C114 the point of injection of a current, the value of which is determined by the output of decoder D2, into one of two identical ladder networks SP, SN, the chosen network being dependent on the polarity bit. In the embodiment described for decoding seven bit numbers, constant current generators G11, G16 controlled by the outputs of decoder D2 give outputs which are in a geometrical progression of ratio (k + 1) 1/64 whilst each mesh of the ladder network gives an attenuation of (k+ 1) 1/4 The decoder may be used in an analogue to digital feedback converter in which first the polarity of the analogue signal to be digitized is determined, that is the value of the bit B1, succeeding stages in the register RG then being switched in until coincidence is achieved.