Patent GB-860181-A (GB)
Title: Improvements in or relating to devices for the selection of electric pulses according
IPC: H03K17/54
Filed: 1957-02-15
Abstract: 860,181. Pulse discriminator circuits. PHILIPS ELECTRICAL INDUSTRIES Ltd. Feb. 15, 1957 [Feb. 18, 1956], No. 5239/57. Class 40 (6). [Also in Group XXXVI] A pulse amplitude discriminator comprises a cathode-ray tube having at least two collector electrodes the pulses being applied to the deflection system of the tube and there being feed-back from at least one of the collector electrodes to the deflector system so that the electron beam has an initial position and at least one other stable position to which it is moved by input pulses falling between defined amplitude levels, the beam is automatically returned to its initial position after having been in the other stable positions for a predetermined period of time. Fig. 1 shows a circuit for counting pulses which fall between given amplitude levels and comprises a cathode-ray tube 1 having deflector electrodes 3, 3<SP>1</SP>, collector or anode 2 and a collector electrode system 4, 5, the electrode 4 being apertured in the line between the cathode and anode 2. Grid 25 enables the cathode-ray beam to be suppressed when required and the anode 2 is connected to a stabilized D.C. source via a counter 6. A feedback circuit is connected from collector electrode 4 to deflector 3 via cathode follower tube 12 and gas tube 14. Bias voltages are chosen so that in the initial position the beam is deflected through a large angle to the right and it is shown that the beam will have two other stable positions through which it may be deflected by input pulses applied via diode 18 to collector 4 and thus via the cathode follower stage 12 to deflector 3. Only pulses falling between predetermined amplitude levels, the limits of which can be pre-set by limiter stage 16, see Fig. 4, cause the beam to be incident on the anode 2 and thus to be recorded by counter 6. At a predetermined time after the beginning of a pulse, device 15 interrupts the beam by applying a negative voltage to grid 25, the beam then reassuming the initial position, 17 being an amplifying stage. Fig. 3 shows a circuit including details of the device 15 shown in Fig. 1. When a pulse appears at the input to diode 18 the grid of tube 12 is driven negative and this is transmitted via tube 19 to cut off tube 22. This does not affect tube 1 as the grid 25 is earthed through diode 30. Capacitor 20 slowly charges through resistor 21 until tube 22 conducts the voltage drop at its anode being transmitted to the grid of tube 1 so that the current in tube 1 is reduced. The voltage at electrodes 4, 5 and thus at the tube 12 increases and this is transmitted through tubes 12 and 19 to tube 22 so that this conducts more highly and its anode voltage falls. This voltage drop completely cuts off the beam in tube 1 until the stray capacitance of the grid of tube 12 is charged so that the grid voltage is reached corresponding to the normal position of tube 1. Diodes 28, 23 conduct and through resistor 31 the grid of tube 1 assumes its normal voltage and the electron beam its initial position. The cut-off period of current in tube 22 and consequently the suppression time of the beam in tube 1 is determined by the time constant R21, C20. By adjustment of the standing bias on the grid of tube 26 shown in Fig. 4 the range of amplitude values between which pulses will be counted may be adjusted, Fig. 5 (not shown).