Device for converting a signal of variable amplitude into pulses of constant frequency and variable duration

摘要

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 11 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 31 applied to a valve having a threshold bias 4 so that the anode circuit is energized with pulses a1, b1, the variation in duration of which is strictly proportional to the value of the signal voltage at equal intervals of time t1, t2, t3. 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.