GB740021A - Improvements in or relating to circuits for producing pulses - Google Patents

Abstract

740,021. Pulse generating circuits. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Nov. 25, 1953 [Nov. 28, 1952], No. 32724/53. Class 40(6). A pulse generating circuit comprises a pulse generator from which a positive voltage step is derived and applied to the control electrode of an amplifier which has a reflecting delay line in its output circuit so that after a time interval equal to twice the transit time of the delay line the voltage step is terminated. Fig. 1 shows a pulse generator comprising a multivibrator 1, 2 and an amplifying valve 12 having a shortcircuited delay line 14 connected across its cathode load resistor 13 which matches the characteristic impedance of the line. When the multivibrator is in the state when valve 2 is cut off a positive step voltage is applied to the amplifier stage 12 and thus across resistor 13. After a time equal to twice the one-way transit time of delay line 14 a negative step voltage is reflected back across resistor 13 to render valve 12 heavily conducting so that its grid/cathode circuit presents a low impedance compared with resistor 8 and a voltage drop is produced at the anode of valve 2. This drop in voltage cuts-off valve 1 and renders valve 2 conductive, the resulting fall in its anode voltage terminating the initial positive step-voltage across resistor 13. Thus a curbed pulse is produced across resistor 13, Fig. 2 (B), not shown, which if differentiated provides two positive pulses separated by a period equal to twice the oneway transit time of delay line 14. The valves 1, 2 and 12 may be replaced by transistors, in the case of the amplifier stage, the emitter collector and base electrodes corresponding to the cathode, anode and control-electrodes respectively. In a modification shown in Fig. 3 the multivibrator circuit of Fig. 1 is replaced by the grids 16 and 17 of pentode 15 connected as a blocking oscillator and the oscillatory effect is controlled by the amplifier 25 being connected to the suppressor grid of pentode 15. The delay line 30 is in this case open-circuited at its distant end so that pulses are reflected without reversal of polarity. In a further modification the multivibrator circuit comprises a triode and pentode valve, the amplifier stage controlling the multivibrator by connection to its suppressor grid.