Patent GB-1434813-A (GB)
Title: Transmission system
IPC: H04M3/02
Filed: 1973-06-21
Abstract: 1434813 Companded delta modulation PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 21 June 1973 [24 June 1972] 29534/73 Heading H3H In a companded delta modulation system in which the comparison signal is generated from the transmitted pulse train in a dynamic control device utilizing a shift register having at least three elements, (14, 15, 16), a signalling generator for transmitting a signalling signal to the receiver is controlled by a clock generator (5) and comprises a cascade arrangement of at least one modulo-2 adder (36) and at least one shift register element (37) connected to the output of the shift register elements (16) in the dynamic control device, the output of shift register element 37 being connected to one input of modulo-2 adder (36) and to one terminal (40) of change over switch (38), the other input to which is from the pulse code modulator 5 and the common terminal of which is connected as input to shift register 14. The signalling signal generated is a 15-digit word. The system output 10 is taken from between register stages 14 and 15. The receiver comprises a signalling signal detector which generates a series of pulses of the same polarity on receipt of the signal. Transmitter (Fig. 1).-A speech signal from (1) is band pass filtered at (2) and subtracted from the comparison signal at (4). Clock pulses from (5) are passed by pulse code modulator 6 when the output of (4) has a predetermined polarity, shaped at 8 and passed via clocked register stage 14 and amplifier 9 for transmission. The pulses also pass through register stages 15 and 16 and the pulses contained in the three stages are sampled by logic circuit 17 which produces an output when all the pulses are zero or one. This pulse output is integrated at 24 and used to amplitude modulate the output pulse train at 11, the train thus being integrated at 7 and applied to 4 as the comparison signal. When switch 38 is switched to terminal 40, the signalling generator comprising register stages 14, 15, 16 and 37 and modulo 2 adder 36 generates the series 100011110101100 in synchronism with clock 5. Receiver (Fig. 2).-Input pulses at 25 are shaped at 26, amplitude modulated by the locally generated dynamic control voltage at 28, integrated at 29 and the resulting signal is filtered and fed to loudspeaker 32. The signal is also applied to shift register stages 14-16 and logic circuit 17 detects all 0 or all 1 in these stages and provides a pulse which is integrated at 24 and used as the dynamic control voltage. The signalling signal recognition device comprises the register stages 14-16 plus a further stage 43 and two modulo 2 adders 42 and 44. This circuit generates a train of like pulses in response to the correct signal and this train is integrated at 45 and the integrated signal will, if the input is correct, exceed a threshold 46 and operate signalling device 35. In an alternative embodiment the signalling signal detector comprises fifteen cascade stages and the output of each stage is connected, through an inverter if necessary to an adding circuit, the output of which exceeds a threshold if all, or the desired number of bits of the signal are correct.