Trigger circuit

摘要

724,837. Pulse-generating and discriminating circuits. ATOMIC ENERGY OF CANADA, Ltd. April 15, 1953 [April 28, 1952], No. 10334/53. Class 40 (6). In a triggered pulse generator, feedback is arranged over a biased rectifier from a dynode to the control grid, the bias allowing the tube to operate under class A conditions. A second feedback circuit for D.C. is arranged over a second valve to ensure constancy of operation. The input pulse may be fed over a biased rectifier to give a discriminating action. In the absence of an input pulse, tube V1 conducts to the dynode and feedback occurs over capacitor C3 and the self-capacity of rectifier X2; the attenuation due to the ratio of control grid to cathode capacity to rectifier self-capacity being such that the loop gain is less than unity. The standing potential of the grid is determined by that of the cathode of tube V2 since rectifier X3 is conducting and the potential of the grid is determined by resistor R10, R12 connected to the anode-feed resistors R1, R2 of valve VI. A rise in grid potential of valve V1 results in a fall in the anode potential which is transmitted by valve V2 operating as a cathode follower to reduce the variation in the grid potential of valve VI. The rectifier X2 is biased to its non-conducting state by a potential derived from the potentiometer R13, the setting of which determines the sensitivity of the device. A positive-going input pulse of sufficient amplitude causes rectifier X2 to conduct due to the resulting rise in dynode potential, the loop gain becoming greater than unity. Heavy current flows from the cathode and maintains saturation between dynode and anode, the rise in dynode potential carrying the control grid into the grid-current region. The control grid and cathode currents then fall with the loop gain less than unity. When the flow of current is insufficient to maintain dynode saturation, the control grid becomes effective and the loop gain exceeds unity, the rectifier becoming non- conductive during this period of operation, the feedback being maintained by its self-capacity. By biasing the rectifier X1 by a potential from potentiometer R15, the circuit may be used as a discriminator. The self-capacitance of the rectifier X1 may be minimized by feeding a negative push-pull input over a capacitor C11 and resistor R19 equal to the self-capacity and back-resistance of the rectifier.