GB628555A - Improvements in or relating to signalling systems employing pulse-width modulation - Google Patents

Abstract

628,555. Pulse modulation ; pulse generating circuits. PHILIPS LAMPS, Ltd. June 6, 1946, No. 17292. Convention date, Sept. 25, 1945. [Classes 40 (v) and 40 (vi)] A signal voltage 1, Fig. 2, of variable amplitude to be transmitted is converted into a wave 1<1> discontinuously changing at equal time intervals to the value of the signal voltage at these instants and a sawtooth voltage of same frequency as the discontinuous changes added to the wave, and the combined voltage 3<1> applied to a valve having a threshold bias 4 so that the anode circuit is energized with pulses a<1>, b<1>, the variation in duration of which is strictly proportional to the value of the signal voltage at equal intervals of time t<1>, t<2>, t<3>. The discontinuous changes take place during the fly-back periods of the sawtooth voltage so that the pulse duration modulation may extend over the whole interval between pulses. The signal voltage is applied through a transformer 7, Fig. 3, to a pair of valves 5, 6 with reciprocally coupled anodes and cathodes and at periodic intervals when the valve grids are driven positive by short pulses derived from the saw-tooth voltage, a voltage is induced in an output condenser 8 equal to the signal voltage of these intervals, and is retained by the condenser between pulses if the resistance 9 is of high value. The ends of the pulses in the anode circuit of a threshold bias stage (Fig. 5, not shown), may be differentiated to produce short pulses of opposite polarity, one set of which is equi-spaced and may be suppressed and the other set of which is phase modulated in accordance with the original signal and may be used to modulate a carrier wave. Specification 594,566 is referred to.