Patent GB-1158809-A (GB)
Title: Improvements in or relating to transmission systems for the transmission of information by means of pulse signals
IPC: H04L25/24
Filed: 1966-10-28
Abstract: 1,158,809. Data transmission systems; pulse signalling. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 28 Oct., 1966 [2 Nov., 1965], No. 48456/66. Headings H4L and H4P. In a pulse code transmission channel the coding of the signals is changed at two or more of the repeater stations along a line, with the object of reducing cumulative errors due to jitter. As described, a transmitting station 2, Fig. 8, sends unipolar P.C.M. signals on a line 1 to a first repeater station 5 which comprises an equalizing network 9, a pulse regenerator 13, a code converter 33, and an output amplifier 11. The input to the pulse regenerator 13 is fed in parallel to a bi-stable trigger circuit 20 and to a clock pulse generator 23, the outputs from 20, 23 being connected respectively to the two inputs of a gating device 17. The clock pulse generator consists of a limiter, a resonant circuit of clock frequency, a 90 degree phase shifter, and a pulse generator, in series (Fig. 2, not shown). The regenerated output pulses from the gating device 17, Fig. 8, are fed to one input of an exclusive-or element 70, whose output is fed to its second input through a delaying network 71 having a delay time T, where T is the clock pulse period. The incoming regenerated pulses are thus recoded (Figs. 9z, 9x, not shown) and, after amplification, are passed to the next section of the line 1, Fig. 8. Similar regeneration and recoding is effected at further repeater stations 6, 6<SP>1</SP> and the signals are received at a station 7 which comprises an equalizing network 15, a pulse regenerator 16, an inverse code converter 35, and a reproduction device 8. The output from the regenerator 16 is fed through delaying networks 72, 73, 74, each having a delay time T, and interposed exclusive-or elements 75, 76, 77, to the device 8. Second inputs to the exclusive-or elements are provided by direct connections to the output of the regenerator 16, and in this way the pulse pattern to the device 8 is restored to that originally sent from the station 2. Means are described for calculating whether or not an exclusive-or element should be interposed between any particular pair of delaying networks in the inverse code converter. The exclusive-or elements used in the system may each comprise two transistors (62), (63), Fig. 7 (not shown) whose emitters are crossconnected through resistors (68, 69) and whose collectors are directly connected together and to a power supply through a resistor (64). Inputs are to the emitters, and output from the commoned collectors. In another embodiment, the unipolar pulses in stations are converted to bi-polar form for transmission, and the inverse code converter is at the transmitting station. As described for a station with three repeater stations 39, 40, 41, Fig. 4, the inverse code converter 59 at the transmitting station 37 comprises an exclusive-or element 60 having a delaying network 61, with a delay time 4T, connected to its output and with its inputs connected, respectively, to a pulse generator 54, and to the output from the delaying network 61. Unipolar to bi-polar conversion is effected by a unit 56 which comprises a linear difference producer 57 having as inputs, respectively, signals directly from the inverse code converter 59, and those signals after passing through a T/2 delaying network 58. At the repeater stations the incoming bi-polar signals are converted to unipolar form by full-wave rectifiers 46, and a similar rectifier 53 is provided at the receiving station 38. The repeater stations also have pulse regenerators 44 and unipolar to bipolar converters 47, which are similar to the converter 56 at the transmitting station 37. A rectifier 46 and a unipolar to bi-polar converter 47 constitute a code converter 45 such that, for example, if the signals sent to line by the transmitting station 37 are as in Fig. 5a (not shown), those sent to line by the first repeater station 39 will be as in Fig. 5f (not shown).