Patent GB-702638-A (GB)
Title: Improvements in or relating to systems of telecommunication employing coded pulse groups
Inventor: PAGES ANDRE PAUL
IPC: H03M1/00
Filed: 1952-04-10
Abstract: 702,638. Pulse code modulation circuits. SOC. ALSACIENNE DE CONSTRUCTIONS MECANIQUES. April 10, 1952 [May 17, 1951], No. 9308/52. Class 40 (5) Relates to pulse code modulation systems, of the kind described in Specification 661,808, in which a code group of n pulses is selected, according to the amplitude of the signal sample to be transmitted, from a binary pulse sequence such as 0100011101, when n=3, where 1 is represented by a pulse and O by the absence of a pulse. According to the invention, this pulse sequence and a step-wave whose levels successively reproduce the 2n possible amplitudes of the wave to be transmitted are both produced during the storage period of each signal sample and the group of n pulses, commencing at the instant when the amplitude of the step-wave goes through the value of the signal sample, is selected and transmitted after the pulses have been staggered to produce predetermined time intervals therebetween. As shown, a coding tube 4 of the type described in Specifications 661,808 and 701,347 is controlled by the sawtooth generator 5 which is locked to the master pulse generator 1. The tube 4 produces for each sawtooth cycle the coding pulse sequence at electrode 404 and a sequence of regular pulses at electrode 406. The wave to be coded is derived from circuit 2 and applied to a sampling and storing circuit 3, under the control of the pulse generator 1, the stored samples being applied in succession to the anode of a comparator diode 901. A circuit 8, similar to circuit 3, produces the comparison step-wave, being fed with the sawtooth wave from circuit 5 and the regular pulses from electrode 406 of the tube 4 and the stepwave is applied to the cathode of diode 901. When the potential of the cathode of diode 901 falls below that of the anode which occurs once per stored sample interval, the diode conducts to enable the blocking oscillator 902 to operate. The resulting sharp positive pulse at its anode is differentiated in circuit 904, 905, and a positive pulse is fed to conductor 907 through valve 906. The code pulse sequence from electrode 404 of tube 4 is fed to a tapped delay line 101, 101<SP>1</SP>, so that all the code groups of three digits appear successively set up at the three tapping points 103, 103', 103<SP>11</SP>. These points are connected to sampling and storing circuits 11, 11<SP>1</SP>, 11" respectively similar to circuits 3, 8. The storage condensers are initially brought to the "no pulse condition by a control pulse over lead 101a from generator 1 and, subsequently, the pulse on conductor 907 effects the transfer of the appropriate code pulses from the delay line tappings to the storage condensers. The signal pulses for the outgoing line 15, appropriately delayed by networks 13, 13', 13" respectively, are generated by differentiating circuits, connected to the storage condensers in circuits 11, 11', 11<SP>11</SP>, which respond to the sudden voltage variation due to a code pulse transfer to a condenser. The sampling and storing circuits 3, 8, 11, 11<SP>1</SP>, 11" which are similar, comprise in the case of circuit 3, for example, two series-connected valves 301, 302 which are normally blocked and a storage condenser 304 connected between their junction and earth. Pulses from generator 1 over lead 303 render the valves conducting to adjust the voltage on condenser 304 to a value depending upon the instantaneous value of the signal applied to the grid of valve 301. The valves 306, 307 amplify the potential of condenser 304.