Patent GB-721818-A (GB)
Title: Electric pulse code communication systems
IPC: H04B14/04
Filed: 1953-01-30
Abstract: 721,818. Pulse code modulation systems. STANDARD TELEPHONES & CABLES, Ltd. Jan. 30, 1953 [Feb, 1, 1952], No. 2741/53. Class 40 (5). To expand the amplitude range, substantially exponentially, of the decoded amplitude modulated pulses derived from pulse code modulated signals, a characteristic of the code signal is used to determine to which of a pluarlity of amplifiers having different gains the decoded pulse is applied. When a standard binary code is used, defining positive and negative signal amplitudes, measured as increases and decreases from the middle of the range of values, the characteristic of the code signal used is the position of the second pulse occurring in the group, after those groups representing negative amplitude levels have undergone a preliminary phase inversion. In one embodiment using this code in the form of six-digit groups representing thirty-two positive and thirty-two negative amplitude levels, the signal source 1, Fig. 1, controls a timing wave source 11. The latter controls a pulse generator 10 feeding gate circuits 9, 13. Circuit 9 is normally closed but opens during the first digit interval while circuit 13 is normally open but closes during this interval. The presence or absence of a pulse in this interval determines over lead 6a whether the remaining five digits pass to the de-coder 2 direct or after phase inversion in circuit 3 and over lead 6b whether the expanded output is passed direct to the utilization circuit or after phase inversion in circuit 4. If the pulse is present electronic switch 6 is operated to cut out the inverting circuit 8. The de-coded pulse from circuit 2 is fed in parallel to five amplifiers I... V which are normally cut off but are unblocked in turn by the first pulse occurring in the five. digit group reaching the coder. This pulse is passed by the normally open gate circuit 14 to unblock the amplifiers I ... V at digit intervals determined by delay circuits 18 ... 21. The gate 14 is closed, after the first pulse has passed, by a flip-flop circuit 16 triggered by the same pulse after a delay of one digit interval in circuit 15. At the end of each code group a pulse on lead 12 from the timing wave source 11 restores to normal the electronic switches in circuits 3, 4 and the flip-flop circuit 16. It is shown that the de-coded pulses corresponding to levels 48 to 63 and 0 to 15 are amplified in amplifier V, levels 40 to 47 and 16 to 23 in amplifier IV, 36 to 39 and 24 to 27 in amplifier III, 34, 35 and 28, 29 in amplifier II and 30 to 33 in amplifier I. The gains of these amplifiers are different, that of I being the smallest and V the greatest and the values rising exponentially. In an alternative embodiment a normal six-unit de-coder produces the amplitude modulated pulses for expansion, only one phase inverter being required, Fig. 4 (not shown). When a cyclic progression code is used, the second digit signals are all inverted before the selection of the second pulse occurring in the group takes place, Fig. 3 (not shown). Specifications 644,935 and 652,212 are referred to.