Patent GB-621869-A (GB)
Title: Improvements in or relating to thermionic valve circuits for causing abrupt changes in current and/or voltage
IPC: H03K3/43
Filed: 1946-05-27
Abstract: 621,869. Sawtooth or pulse generating circuits. PHILIPS LAMPS, Ltd. May 27, 1946, No. 16014. Convention date, March 13, 1942. [Class 40 (vi)] A circuit for generating abrupt current and/or voltage variations comprises a grid controlled secondary-emission valve, the grid and auxiliary cathode circuit impedances being mainly resistive and regeneratively coupled so that a stable operating point can be obtained only with grid voltages which are less negative than a first limit value or are more negative than a second limit value (at which the anode current is substantially suppressed), the control grid and cathode being connected by a diode rectifier to limit any variation of the control grid voltage beyond a given value. In Fig. 4, the auxiliarycathode 4 and grid circuit 3 are regeneratively coupled, the grid bias being adjusted to correspond to the limit value I or II, Fig. 3. When a voltage pulse of suitable polarity is fed to the input terminal, the operating point changes from I to II or vice versa, an abrupt voltage change being produced across load resistor 10. A pulse of very short build-up time is produced by the provision of diode 30 and battery 31 between the control grid and cathode circuits, the control grid voltage thus being prevented from rising above a limit value governed by the voltage of battery 31 and shown at I<1> in Fig. 3. Since the diode characteristic shows greater curvature near the zero point than the gridcathode characteristic of valve 1, the effective slope at the limit value I<1> changes more rapidly than that at I, thus causing the operating point to change very quickly from I<1> to II. A similar effect for the part of the curve in the neighbourhood of limit value II is obtained by a gas discharge valve 32, which acts as a constant voltage device between resistors 14 and 25, thus ensuring that when the anode current of valve 1 is suppressed the auxiliary cathode voltage does not fall below a value governed by gas discharge valve 32 and battery 12 and thus that the' current through potentiometers 14, 25 is always considerably larger than the auxiliary cathode current. The provision of capacitor 33 enables a sawtooth voltage output to be obtained. The Specification as open to inspection under Sect. 91 described a modification, Fig. 4 (Cancelled, not shown), in which the gas-filled valve is replaced by a normal resistor, and the capacitive coupling between auxiliary cathode and control-grid is omitted. In a further modification, Fig. 6 (Cancelled, not shown), the input signal is applied via oppositely-poled diodes, thus enabling the circuit to operate with pulses of either polarity; negative feed-back being introduced by an unshunted cathode resistor. In another modification, Fig. 7 (Cancelled, not shown), the circuit is rendered self-oscillatory by using a capacitive coupling between the auxiliary-cathode and control grid and adjusting the value of grid-bias. The circuit may be synchronized by incoming signals. This subject-matter does not appear in the Specification as accepted.