Patent GB-742661-A (GB)
Title: Improvements in or relating to discriminators and pulse amplitude analysers
Filed: 1953-02-16
Abstract: 742,661. Pulse amplitude discriminator circuits. FARLEY, F. J. M. Dec. 23, 1953 [Feb. 16, 1953], No. 4316/53. Class 40 (6). A pulse amplitude analyser or discriminator circuit of the type in which an output pulse is obtained each time that a pulse in a series has an amplitude exceeding a pre-determined datum level comprises an input amplifier and a discriminator circuit, the amplifier consisting of two discharge-tubes connected with their anode/ cathode paths in series, the input pulses being applied between the grid/cathode path of one tube and the output being derived from between the cathodes of the two tubes. The analyser preferably comprises two discriminators operating at a lower and upper datum level respectively so that when the input pulse amplitude exceeds the upper datum level a " veto pulse " is generated and suppresses the output pulse of the discriminator having the lower datum level. The Figure shows a pulse amplitude analyser comprising an amplifier V1, V2, V3, V4, a first discriminator V5A, V5B, V9B, a second discriminator V6A, V6B, V9A, an anti-coincidence mixer stage V8A, V8B, a veto-pulse generator V7A, V7B, a trigger circuit V10 and an output stage V11. Positive-going input pulses are applied at 11 to the long-tailed pair V1, V2 and if they exceed in amplitude the pre-selected grid bias applied to the grid of V1 from the stabilized bias source across R7, R8 produce a negative pulse at the anode of V1 which when it exceeds a predetermined minimum value passes via biased diode d1 to the grid of V3. The signal across the anode load R15 is applied to V4 so that an output signal is produced between the cathode of V4 and earth. The amplifier has two feedback loops the first which operates during the trailing edge of the pulse at the anode of V1  and is via V3, V4 and d2 and the second from the cathode of V4 to the grid of V2 via network R12, R13, C7, C8, a phase advancing network C9, R16 ensuring H.F. stability. The positive output pulse from the amplifier V1-V4 is applied to the two discriminators' which each comprise basically a trigger-pair circuit V5A, V5B and V6A, V6B respectively, which are arranged to have a small " backlash " by provision of tubes V9B, V9A respectively, which on the occurrence of the trailing edge conduct and prevent the commoned cathodes of the tubes V5A, V5B and V6A, V6B respectively from falling more than, say, 10 volts below their original steady level. The negative pulse across load resistor R30 of tube V9B when the discriminator resets is used to initiate generation of the final output pulse. The triggerpair circuits V5A, V5B and V6A, V6B have their datum levels determined by the bias applied to the grids of tubes V5B and V6B via diodes d4 and d5 respectively, the former being continuously adjusted over a small range by resistor R45 and the latter in steps by switch S2. If the amplitude of an input pulse is such that both discriminators are operated the # vetopulse " generator comprising trigger-pair V7A, V7B generates a # veto-pulse," Fig. 4 (not shown), which has a larger amplitude whilst both discriminators are triggered than when one only has reset. The output from the discriminator having the lower datum level and the " veto-pulse " from tube V7B are applied to the grids of tubes V8B and V8A in an anti-coincidence mixer. In the absence of a " vetopulse " a negative pulse is transmitted from the anode of tube V8A to tube V10 and thus to the output stage V11, but when a "vetopulse " is present this output pulse is suppressed. If it is required that the analyser shall function as a simple discriminator, diode d6 is earthed via switch S1 so that no " veto-pulse " is generated. The meter VM may be calibrated corresponding to the lower datum level of the analyser and the range may be extended by insertion of an external battery and/or meter in links 51, 52.