GB747222A - Method and device for compression and expansion for electric pulse communication systems - Google Patents

Abstract

747,222. Pulse modulation systems. COMPAGNIE INDUSTRIELLE DES TELEPHONES. March 15, 1954 [March 23, 1953], No. 7404/54. Class 40 (5). Relates to instantaneous compression and expansion circuits for compandor systems using duration-modulated pulses. In the compression circuit rectangular pulses, Fig. 3, from a source 17, 17<SP>1</SP>, Fig. 10, are modulated in amplitude in circuit 15 by a voice current source 12, 12<SP>1</SP> and applied to the clipper valves 14, 18, through transformer 13. The transformer 11 adds to the modulated pulses a voltage from a source 10, 10<SP>1</SP> of the " compression " waveform APMQB, Fig. 4, to produce a waveform lying between the extremes I, II. The clipping of this waveform between the voltage limits a, a<SP>1</SP>, and b, b<SP>1</SP>, by valves 14, 18, produces durationmodulated pulses whose trailing edges lie between the extreme times t1, t2 and which have been modified by the compression waveform. The latter may be produced by applying a sine wave, Fig. 9(a), to a squarer valve 2, Fig. 8, from a source 1, to produce the square wave of Fig. 9(b) across resistance 4. The latter is shunted by a short-circuited delay line 3 of such dimensions as to modify the square wave voltage to assume the form of alternate positive and negative pulses, Fig. 9(c). The negative pulses are removed by the biased valve 5 and the output resistance 8 is shunted by a shortcircuited delay line 7 to produce the closelyspaced pairs of pulses, Fig. 9(a). These pulse pairs are converted to the desired waveform, by the low-pass filter 9, which is connected to the modulator terminals 10, 10<SP>1</SP>. The expansion circuit at the receiver comprises a gate circuit 21, Fig. 11, which is opened by the signal pulses, on terminals 22, 22<SP>1</SP>, to allow parts of an auxiliary locally-generated sawtooth wave, on terminals 20, 20<SP>1</SP>, to pass to the low-pass filter 23 and demodulated-signal amplifier 24. The auxiliary sawtooth wave JLH 0 NR, Fig. 6, straddles the trailing edge G 0 O 0 of the unmodulated received pulses, the extreme modulated positions of the latter being G1, H1 and G2, H2 so that the variable portion of the gate circuit output energy has the desired expansion characteristics due to the variable triangular portions H2, K2, H0 and HO, K1, H1. The sawtooth wave may be replaced by a rectified sine wave, Fig. 7 (not shown). Specification 650,886 is referred to.