GB631171A - Improvements in and relating to circuits for converting a periodic voltage into a voltage of stepped wave-form - Google Patents

Abstract

631,171. Converting and phase changing. PHILIPS LAMPS, Ltd. June 6, 1946, No. 17293. Convention date, Oct. 1, 1945. [Class 38 (ii)] [Also in Group XL (c)] In a circuit for converting a periodic voltage into a stepped voltage, particularly for demodulating phase modulated pulses, use is made of a secondary emission valve 1 (Fig. 1). The secondary emission electrode 5 is connected to the cathode 2 via a series connection of a condenser 8 shunted by a resistance 7, a source of supply 9, supplying the voltage to be converted, and a source 10 of D.C. voltage. The anode 6 is connected to the screen grid 4 and to the source of supply 10, so that the anode has the same D.C. voltage with respect to the cathode as the secondary emission electrode 5. The impedance between the cathode and electrode 5 of the valve 1 is variable, the voltage, current curve of electrode 5 being as shown in Fig. 2. The time constant of the charging circuit of the condenser 8 comprising the source 10, the variable impedance and the source of supply 9 is made small so that the condenser 8 is readily charged when the valve conducts, whereas the time constant of the condenser 8 and resistance 7 is large so that the condenser remains charged when the valve is non-conducting. Phase-modulated pulses 19 (Fig. 5) are applied to the grid 3 of the valve via a condenser 12, and the source 9 generates a saw tooth wave 20 of the same frequency as the pulse recurrence frequency, the centre of the inclined edge of the sawtooth wave coinciding with the position of unmodulated pulses. The valve is normally cut-off, but when a pulse is applied to the grid allowing the valve to conduct the condenser 8 is charged (or discharged) to the instantaneous value of the sawtooth wave 20. It then remains charged (or discharged) until the next pulse is applied, thus producing the envelope 21, which when passed through a low pass filter produces the wave 22. If the pulses are unmodulated then a steady D.C. may be derived from the condenser circuit. Should the source 9 drive the secondary emission electrode 5 negative with respect to the cathode, then the condenser may be charged in the opposite sense as indicated by the characteristic curve of Fig. 2. In a modification the source of supply 9 may be contained in the anode 6 lead (Fig. 7, not shown). In a further embodiment phase-modulated pulses are first converted to a variable sawtooth wave, the mean value of which corresponds to the signal, and the variable sawtooth then smoothed by using it as the source 9 and applying the modulated pulses to the grid 3 (Figs. 8 and 9, not shown). Specification 628,551, [Group XL (c)] is referred to. In the Specification as open to inspection under Sect. 91, a tetrode may be used, employing the screen grid as the secondary emission electrode (Fig. 8, Cancelled, not shown). This subject-matter does not appear in the Specification as accepted.