Patent GB-766974-A (GB)
Title: Repetitive-linear-sweep-signal generator
IPC: H03K4/22
Filed: 1955-03-07
Abstract: 766,974. Discharge tube and transistor pulse and sawtooth circuits. HAZELTINE CORPORATION. March 7, 1955 [April 9, 1954], No. 6630/55. Class 40(6) In a generator, a bias circuit normally maintains a first electronic device in a state of low conductivity and a second device in a state of high conductivity, a triggering circuit increasing the conductivity of the first device and a circuit connection being arranged to maintain the second device in low conductivity during the period that the first device is in high conductivity to develop a sawtooth. The circuit may employ thermionic discharge tubes or transistors and the bias circuits may be adjusted to make the circuit selfrunning. Discharge tube circuit. A first tube 22, Fig. 1, is biased off by the anode current of the second tube 23 passing through resistor 24, diode 25 and resistors 26, 27, the grid of the tube 23 being returned over resistor 32 to the power supply to maintain the tube in a fully conducting state. Since substantially no anode current flows in tube 22, the anode potential is near the supply so that diode 29 has little or no bias applied to it. Negative triggering pulses A, Fig. 2, from generator 12 are passed through diode 29 and capacitor 30 to reduce the voltage on the grid of tube 23, curve B. The resulting fall in anode current, curve C reduces the negative bias on tube 22 which passes anode current curve F, its potential falling in accordance with curve E. Since the impedance of resistor 33 is much greater than that of tube 22 when conducting and resistor 24, tube 23 operates as a Miller integrator. The run-down occurs inthe normal manner until the potential of the cathode of tube 22, curve D falls sufficiently for the diode 25 to conduct and the process is arrested. The grid potential of tube 23 then rises causing heavy anode current to flow which biases off tube 22 to restore it to its normal condition. Capacitor 30 recharges over resistor 33 and the grid-cathode path of tube 23. The circuit may be made free-running by reducing resistor 24 so that during the recharging period the anode of tube 22 rises sufficiently for the tube to be rendered conducting again. A square wave, curve G is developed across resistor 26 and may be used for gating. The duration of the sweep may be varied by closing switch 27b and adjusting resistor 27a to alter the bias potential. Transistor circuit. A second transistor 41, Fig. 3, conducts to maintain the collector near earth potential, curve J, Fig. 4, the current through resistor 44 and diode 43 maintaining the emitter of the first transistor 40 negative with respect to the base. curve M so that the transistor is cut off. A positive triggering pulse curve H fed in over diode 50 and phase reversed by transformer 48 reduces the emitter potential, curve I and after a delay, possibly due to hole storage, reduces the collector current J so that the collector potential K falls thereby allowing the transistor 40 to conduct, the diode 43 cutting off due to the fall in emitter potential, curve L. The capacitor 46 discharges through the primary of transformer 48, base-collector path of transistor 41, resistors 44, 53 and transistor 40, any deviation from linearity causing a variation in the emitter-base potential of transistor 41. The output sawtooth curve N appears at the collector of transistor 40. When the emitter potential of transistor 40 rises sufficiently for the diode 43 to conduct again, curve L, the discharge process is arrested and capacitor 46 recharges through resistor 47 and the primary of transformer 48, the induced current in the secondary maintaining full conduction in transistor 41 and a low collector potential to maintain transistor 40 substantially cutoff.