GB828398A - Improvements in or relating to decoding arrangements for electric pulse code modulation systems - Google Patents

Abstract

828,398. Electric selective signalling systems. STANDARD TELEPHONES & CABLES Ltd. April 18, 1958, No. 12347/58. Class 40 (1). [Also in Groups XL (a) and XL (c)] A de-coding arrangement employing a digit pulse code adapted to represent m different amplitude levels of a signal wave, comprises a cathode-ray tube having an assembly of m decoding elements corresponding respectively to the said amplitude levels, means controlled by the digit pulse combination representing any given level for directing the electron beam on to the decoding element corresponding to the given level, and means for deriving from the last-mentioned decoding element an output voltage or current representing the given element. As described in decoding a six-bit word pulses representing the six bits are applied to terminals 1 to 6, Fig. 1, to cause the cathode-ray tube beam to pass through a particular aperture of an apertured mask 21, then through a corresponding aperture in a " perveance plate " 22 to a collector plate 23 to cause an output at a terminal 35, each aperture of the perveance plate being arranged, either by being covered by a wire grid of an appropriate mesh or by being appropriately dimensioned, to have a different perveance whereby the electron charge that actually reaches the collector plate is different for each aperture so that the amplitude of the output pulse on terminal 35 is representative of the particular aperture and therefore of the particular word being decoded. In a modification the array of different perveance apertures in the perveance plate 22 is replaced by an array of series-connected resistance strips (Fig. 8, not shown), the collector plate 23 is omitted and an output is taken from the seriesconnected resistance strips. This modification is shown in principle in Fig. 7: the series-connected resistance strips can be regarded, with the cathode-ray tube beam, as forming a potentiometer, giving, as before, an amplitude analogue at a terminal 35 of the word being decoded. The bits of the word being decoded can each have three or more amplitude significant states. Reference has been directed by the Comptroller to Specification 652,846.