GB1105717A - Non-linear decoder - Google Patents

Abstract

1,105,717. Selective signalling. INTERNATIONAL STANDARD ELECTRIC CORPORATION. 8 Sept., 1966 [15 Sept., 1965], No. 40129/66. Heading G4H. In a digital-to-analogue converter having a non-linear characteristic comprising fourteen straight line segments (Fig. 2, not shown) divided into seven symmetrically disposed pairs each segment of a pair having the same slope, firstly the top most significant four bits of a seven-bit input signal are decoded to produce a voltage corresponding to the bottom end point of a particular segment, secondly the remaining three bits are scaled in accordance with the slope of the selected segment and decoded linearly, and finally the two voltages obtained are summed. The two centre line segments (which have the same slope) are each selected by two different combinations of the top four bits. Thus, effectively they are selected by particular combinations of the top three bits, and for these two straight line segments the bottom four bits are decoded linearly; i.e., in general each straight line segment is divided by eight equally spaced points, but the centre two are each divided by sixteen. The top four bits are arranged, by switching networks not described, to cause 0, 1 or 2 units of current to be injected into the top six rungs of a ten-rung resistor ladder attenuator, so that its output voltage corresponds to the bottom end of the particular straight line segment which they represent. The bottom three bits (four of the centre segments) are arranged, by switching networks partly described (Fig. 5, not shown), to inject 0 or 1 units of current into a group of three (or four) adjacent rungs of the ladder attenuator, the particular group being selected by the top four (or three) bits, so that the resultant output voltage produced by the ladder is the sum of a voltage representing the bottom end of a segment and a voltage representing a portion within a segment. The use of the decoder in a feedback encoder is mentioned.