Patent GB-646051-A (GB)
Title: Improvements in or relating to electric pulse code modulation systems of communication
Inventor: EARP CHARLES WILLIAM
IPC: H03M1/44
Filed: 1948-02-20
Abstract: 646,051. Multiplex pulse code signalling. STANDARD TELEPHONES & CABLES, Ltd. Feb. 20, 1948, No. 5014. [Class 40 (v)] In a communication system using pulse code modulation, the code being of the simple addition binary type, modulation and demodulation are both effected by a series of two-condition trigger circuits corresponding to the code elements, the circuits being set in the first or second condition in accordance with the code distribution representing the instantaneous signal amplitude. Transmitter.-The coding device described comprises the trigger triode pairs 1A, 2A ... 1E, 2E, Fig. 1, the grids of which are connected through resistances 11A, 12A ... 11E, 12E to pairs of terminals 9A, 10A ... 9E, 10E. The terminals 9A ... 9E are inter-connected by resistances 17B... 17E and terminals 10A ... 10E by resistances 18B ... 18E. The anodes of each triode pair 1A, 2A ... 1D, 2D are connected to terminals 9B, 10B ... 9E, 10E by resistances 19B, 20B ... 19E, 20E. The signal is applied in push-pull from transformer 15 to terminals 9A, 10A and output terminals 21A ... 21E are connected to the anodes of the right-hand triode of each pair. The first pair of triodes are arranged so that if 1A is cut off and 2A conducting, this condition will reverse when the potential of terminal 9A with respect to terminal 10A changes sign from negative to positive and switch back again when this potential changes sign from positive to negative. The other stages are similarly arranged but are operated by a component of the signal voltage and the output from the preceding trigger stage. The outputs from the stages A ... D are adjusted to correspond with 8, 4, 2 and 1 signal amplitude steps, respectively, and may be positive or negative depending on their individual conditions. Thus at any instant the condition of the five stages is representative of the input signal amplitude. For example, for a signal amplitude of +12.5 steps, circuit A will be in the second condition and 12.5 - 8 steps applied to the circuit B. Circuit B will be in the second condition and 12.5 - 8 - 4 steps applied to circuit C. Circuit C will be in the second condition and 12.5 - 8 - 4 - 2 steps applied to circuit D. Circuit D will be in the first condition and 12.5 - 8 - 4 - 2+1 steps applied to circuit E which will therefore be in the first condition. If the signal amplitude had been negative, then A, B and C would have been in the first condition and D and E in the second. When any stage is in the second condition a relatively high potential appears on the output terminal 21 and is used as a gating potential to allow a corresponding pulse to be emitted in the code group. The code gate circuit, Fig. 2 (not shown), is similar to that described in Specification 646,050. Receiver and multiplexing.-A multichannel transmitter using a common coding circuit for all the channels and a suitable multichannel receiver, similar to those described in Specifications 644,935 and 646,050, are described, Figs. 3 and 4 (not shown). Specifications 535,860 and 644,936 also are referred to.