GB695223A - Improvements in or relating to electric gating devices - Google Patents

Abstract

695,223. Pulse code signalling; valve gating circuits. GENERAL ELECTRIC CO., Ltd. Dec. 14, 1950 [Dec. 5, 1949], No. 30565/50. Divided out of 695,198. Classes 40 (v) and 40 (vi). In an electrical gating device comprising first and second thermionic valves having a common cathode circuit across which is developed the gated signal voltage, a third thermionic valve is connected in the said common cathode circuit and has resistance connected in its cathode circuit, the signal to be gated is supplied to a control grid of the first valve, a gating signal is supplied to a control grid of the second valve, and a signal is supplied to a control grid of the third valve to cause that valve to be relatively highly conducting when the first valve is conducting. The arrangement shown forms part of the pulse code modulation system described in the parent application, the signal to be transmitted being periodically sampled and the condenser 1 charged to the level of each sample in turn. The voltage stored by the condenser 1 is fed to the coding apparatus 2, a train of pulses 4 being supplied to the terminal 3, and the apparatus 2 subtracts the peak amplitude of each pulse 4 from the level stored by the condenser 1 to charge a condenser 5 to the resultant voltage. If this resultant voltage has a value above a pre-determined datum it is required to reduce the level stored by the condenser 1 to that of the condenser 5 before the next subtraction is made, and for this purpose there is provided a gating device comprising valves 7 and 8 whose cathodes are connected to the anode of a pentode valve 12. The voltage stored by the condenser 5 is applied to the grid of valve 7 and a square waveform signal is applied through a diode 15 to the grid of valve 8, a signal of the same waveform but opposite phase being applied to the grid of the pentode valve 12. During positive-going portions of the signal supplied to the diode 15 the valve 8 is conducting and the valve 7 cut off, and the cathode 10 is raised to such a potential that the diode 24 cannot conduct, but during negativegoing portions the condition of valves 7 and 8 is reversed, and the diode 24 conducts to reduce the voltage stored by condenser 1 to that stored by condenser 5. By arranging for the valve 12 to be highly conducting during alternate halfcycles the time during which condenser 1 is discharged to its new value is reduced. The apparatus 2 supplies a positive-going impulse to the diode 16 to block the gating device when the voltage resulting from the subtraction of a pulse 4 from the level stored by condenser 1 falls below the datum voltage.