| 摘要 |
644,892. Pulse generating circuits. PHILIPS ELECTRICAL. Ltd. Nov. 27, 1947, No. 31431. [Class 40 (vi)] A pulse generator comprises a blocking oscillator and a crystal controlled oscillator in one valve stage so that pulses are generated having the frequency and stability of the crystal. Fig. 1 shows a pentode valve in which the cathode and grids 1 and 2 are coupled to operate as a crystal-controlled oscillator, the frequency of which is determined by the crystal 8 and the tuned circuit 10, 11. The grid 3 and anode 5 are coupled to oscillate at a much higher frequency in blocking oscillator manner by means of the circuit 15, 16, 17 and 18. The system oscillates during one half-period of the high natural frequency of coil 15 or 16 either or both of which are timed, grid 3 then blocks, the screen-grid current increases and due to the transitron effect of the inter-electrode capacity which couples grids 2 and 3 the blocking effect is additive and the valve is conductive during only a fraction of each period of the crystal frequency when a highly damped oscillation of very high frequency is produced, Fig. 2b and c (not shown). The time constant of network 17, 18 and the small phase shift due to coil 10 ensure that current passes through the valve only once per period of the crystal frequency. Diode D ensures that passage of charging current to capacitor 17 is not prevented by grid 1 blocking the current flow through the valve. |
