Patent GB-973087-A (GB)
Title: Improvements in or relating to pulse modulation systems
Inventor: THOMAS EDWARD REGINALD
IPC: H04B14/04
Filed: 1961-03-23
Abstract: 973,087. Pulse modification multiplex systems. GENERAL ELECTRIC CO. Ltd. March 23, 1962 [March 23, 1961], No. 10684/61. Heading H4L. A pulse modulation multiplex system comprises means for sampling each channel in turn, means for determining the polarity of the signal and for reversing the polarity, when necessary, to produce unipolar signals, means for charging a capacitor to the amplitude of the sampled signal and for counting the number of constant frequency pulses generated during the time the capacitor discharges to a reference value, the number of pulses counted per unit amplitude of sample signal being greater for low amplitude signals than for high amplitude signals, means for transmitting the number of pulses counted in binary code and for reconstituting the channel signal at the receive terminal. The transmit channels 1 are sampled in turn by a control unit 4 which is supplied from pulse generator 3. The polarity of each sample signal is determined in unit 5 which supplies an output signal to polarity store 7 and to a polarity reversal unit 6. Where necessary unit 6 reverses the polarity of the signal and provides a unipolar sample signal to which a D.G. signal of x volts is added in unit 8. Gate 9 is opened during part of the sampling period and a capacitor 10 is charged to the value of the combined signal. The capacitor discharges through resistor 11 and during the time period from the commencement of discharge to the time the capacitor discharges to a reference value equal to x volts a comparator circuit 12 generates a time duration pulse representing the amplitude of the sample signal which opens a gate 14 whereby pulses from a constant frequency source 15 are counted into a binary six-stage counter 16. Since the time taken for the capacitor to discharge a unit amount is greater when discharging from a small initial amplitude than from a large, the number of pulses counted per unit change in amplitude is greater for sample signals of small amplitude than for large. A pulse signal from generator 19 transfers the count in counter 16 to the first six stages of an eight-stage register 18, the seventh stage of the register receives any stored polarity signal from store 7 and the eighth stage is supplied with a synchronizing signal from unit 22. Clock pulses from generator 23 then transfer the register digits serially to transmit line 24. The frequencies of operation of the various pulse generators 3, 23 and 19 are locked to synchronize the operation of the arrangement. At the receive terminal each pulsed signal is used to reproduce the time duration pulse from which a pulse having a duration which is equal to the difference between the maximum possible duration (the time taken by the capacitor in discharging when charged by a sample signal of maximum amplitude) and the duration of the reproduced time duration pulse. This difference duration pulse determines when the voltage across a capacitor resistance arrangement, similar to that at the transmit terminal, and initially charged to the maximum amplitude, is sampled. The sampled signal is then reversed in polarity, if necessary, and distributed to its appropriate channel in which it is converted by a pulse-lengthening circuit and a low-pass filter to an audio frequency signal. Specification 973,088 is referred to.