Patent GB-694030-A (GB)
Title: Improvements in or relating to pulse code translating circuits
IPC: H03M5/00
Filed: 1950-02-03
Abstract: 694,030. Pulse code modulation. pulse circuits. WESTERN ELECTRIC CO., Inc. Feb. 3, 1950 [Feb. 11, 1949], No. 2840/50. Classes 40 (v) and 40 (vi). For translating groups of pulses in the reflected binary code, as described in Specification 663,872, to corresponding groups in the common binary code, a plurality of input circuits for the applied code elements are connected to a plurality of output circuits by paths which produce in the latter pulses representing the re-entry addition of the pulses in the input circuits corresponding to the reflected binary code elements of the same and higher significance as that of the code element in the respective output circuit. If a pulse represents the digit 1 in the binary rotation and absence of a pulse, the digit 0, then re-entry addition gives the results 0+0=0, 0+1=1, 1+0=1 and 1+1=0. In the embodiment described the terminals 1 ... 7, Fig. 2, have applied to them simultaneously the seven pulse elements of seven-unit reflected pulse code groups. The code element of highest significance is always identical in both codes so that terminal 7 is connected directly to the corresponding terminal 17 of the output terminals 11 ... 17. The other input terminals 1 ... 6 are connected to the corresponding output terminals 11 ... 16 through re-entry adders 18 ... 23 respectively which receive and add the code element from the input terminal and that element fed to the next highest output terminal. In order to compensate for the delays in the adders, to ensure successive additions and a simultaneous production of the output elements, delay circuits 35 ... 31 are interposed in input circuits 1 .. 5 and delay circuits 36... 41 in output circuits 12. .17 respectively. It will be seen that each adder such as 23 has two input circuits 24, 25 and two output circuits 26, 27, the latter conveying the same output code element. An adder circuit comprises four valves 51 ... 54, Fig. 3, the inputs 24, 25 being applied to the grids of valves 51, 52 respectively. Their cathode impedances comprise, in the case of valve 51, a small resistance 55 and large resistance 56 which also form the cathode impedance of valve 53 and, in the case of valve 52, a small resistance 57 and a large resistance 58 which also form the cathode impedance of valve 54. The anodes of valves 51, 52 are connected together and the anodes of valves 53, 54 are connected together and through a common output resistance 59. The grid of valve 53 is connected to the junction of the cathode resistances 57, 58 of valve 52, and the grid of valve 54 is connected to the junction of the cathode resistances 55, 56 of valve 51. The grids of valves 51, 52 are biased positively by sources 65, 66 through D.C. restorers 61, 63 and 62, 64 respectively and negative input pulses are applied to the circuit. In the absence of a pulse at both inputs valves 53, 54 are non- conducting being biased to cut-off by the voltage drops across resistances 55, 57 respectively. If both inputs receive a pulse, the cathodes of all the valves become less positive, but the grids of valves 53, 54 also become less positive and by almost the same amount, so that both valves remain cut off and no pulse is an input pulse is applied to valve 52 only, the developed across resistance 59. If, for example, grid of valve 54 remains at a fixed voltage and its cathode goes less positive until it conducts and maintains the current through resistances 57, 58 to cause cut off of valve 52. The conduction in valve 54 results in the development of a pulse across the output resistance 59 which is connected to the output leads 26, 27. A similar action occurs if an input pulse is applied valve 51 only. In a modification of this circuit, Fig. 4 (not shown), one of the pulse outputs is taken from the anodes of valves 51, 52. In another modification, Fig. 5 (not shown), the grid biases for valves 53, 54 are obtained from independent sources and there is no D.C. grid coupling to the other valves. The valves may be replaced by transistors of the type described in Specification 694,021. Specifications 649,376 and 652,908 also are referred to.