Patent GB-731151-A (GB)
Title: Improvements in and relating to electron discharge valve circuits for generating voltage variations of saw-tooth and rectangular waveform
Inventor: LEVELL DEREK ALFRED
IPC: H03K4/22
Filed: 1950-06-08
Abstract: 731,151. Saw-tooth and pulse generating circuits. COSSOR, Ltd., A. C. May 24, 1951 [June 8, 1950], No. 14369/50. Class 40 (6,). In a saw-tooth or pulse generator of the Miller integrator type a triggering pulse is applied to a control circuit comprising two further valves which have a common cathode impedance, the anode of the second valve being coupled to an electrode of the Miller valve and the control electrode of the third valve being coupled to a control electrode of the Miller valve. In this way the circuit functions with a triggering pulse of small amplitude. Fig. 1 shows a saw-tooth or pulse generator comprising a Miller valve 10 and' cathode-coupled control valves 19 and 20. The control grid of the Miller valve is returned to a positive voltage source at 14 via resistors 12 and 13. In its quiescent state the suppressor grid of the Miller valve is biased negatively so that screen current only flows and anode current flow in valve 20 biases valve 19 to cut-off by reason of the cathode resistors 21, 22. A positive-going triggering pulse applied at 32 is differentiated by network 33, 35 and the resulting negative pulse cuts-off valve 20 so that its anode potential rises and consequently the suppressor grid voltage of the Miller valve 10. Some of the screen grid current in valve 10 is diverted to the anode, the screen voltage rises and thus that of the control grid of valve 19. The resulting cathode current flow in valve 19 biases off valve 20, the action being cumulative so that valve 20 is cut-off and a large positive pulse is applied to the suppressor grid of valve 10. The anode voltage of valve 10 commences to fall and thus " runs-down " linearly in the normal Miller integrator manner until the valve " bottoms " when the screen current increases. This causes the conductivity of valve 19 to be reduced and of valve 20 to be increased until by cumulative action valve 20 is rendered conducting when the anode potential of valve 10 rises to that of terminal 18 at a rate dependent upon the time constant of network 16, 17. The potential at the junction of resistors 21, 22 is such that the suppressor grid voltage of valve 10 is maintained positive during the anode voltage " run-down." A linear saw-tooth voltage is thus produced at the anode of valve 10 and a positive-going pulse is produced at terminal 31, of which the leading edge is coincident with the sharp negative pulse produced by differentiation of the triggering pulse and the trailing edge coincident with the negative pulse appearing at the suppressor grid of valve 10 at the end of the anode " run-down." A pulse of identical waveform to this but in anti-phase is produced at terminal 30. The generator may be made free-running by returning resistor 25 to a positive source and arranging network 24, 25 to have a suitable time constant. In a modification, Fig.: 2 (not shown), a D.C. coupling is provided between the anode of valve 20 and the .suppressor grid of valve 10. In a further modification shown in Fig. 3, the time constant of discharge of ,capacitor 24 is made long compared with " run-down " period of the Miller valve and diodes 39, 40 act as D.C. restorers.