GB1319628A - System for the transmission of analog signals by means of pulse code modulation - Google Patents

Abstract

1319628 Coding and decoding TELECOMMUNICATIONS RADIOELECTRIQUES ET TELEPHONIQUES 3 Aug 1970 [6 Aug 1969] 37330/70 Heading G4H [Also in Divisions H3 and H4] At the transmitter of a coder/decoder samples of an analogue signal are converted to 12 bit digital form S n ...S 1 , S 0 , S -1 ... and expanded to 16 bit form by the addition of two zeros at each end before being fed to a digital filter which at a time t -5 corresponding to the S -5 th digital value provides an output # E = S 5 A 5 + S 3 A 3 + S 1 A 1 + S 0 A 0 + S -1 A 1 + S -3 A 3 + S -5 A 5 where A 1 are the coefficients of the inverse fairier transformation at the instance when the samples S 1 and S -1 occur. The analogue/digital converter is preferably a coarse and fine dual ramp digital voltmeter with coarse and fine counter operating shift registers to feed the 12 bits after expansion to 16 bits to the' filter of Fig. 5 which comprises registers R1-R6 receiving combinations of the coded signals multiplied by the coefficients A5, A3, A1 and A0 such that at time T -5 the contents of register 6 are # E . The filter is connected to a compressor 4 which transmits the PCM signals to an expander 5 in the receiver. At the receiver the signals are transformed in a filter similar to the filter of the transmitter except since in this case S. = 0 there is no multiplication by A 0 . the signals are simultaneously fed to a delay. The delay and filler feed a second filter and delay so that output signals are obtained at four times the frequency of the transmitted coded signals. The PCM signals are converted to # pulse modulated form by subtracting successive code groups and fed to converters 7 one of which is shown in Fig. 7 which using gates P1-P6 enabled far differing numbers of clock pulses deliver a number of pulses corresponding to their weights to an OR gate P7. The gates P7 are connected to integrators to give an output, the mean value of which corresponds to the analogue input to the transmitter.