Patent GB-853413-A (GB)
Title: Improvements in pulse generators
IPC: H03K17/54
Filed: 1957-04-10
Abstract: 853,413. Non-linear amplifier circuits. INTERNATIONAL BUSINESS MACHINES CORPORATION. April 10, 1957 [April 12, 1956], No. 11678/57. Class 40(6). A pulse generator comprises a power stage having a negative feedback circuit connected between its output and an AND circuit in its input the feedback being operative only when the output from the stage reaches a predetermined level. Fig. 1 shows the application to a circuit in which it is required to generate current pulses in a magnetic core array 1. A selecting pulse is applied at terminal 5 and a timing pulse at 6 to the input of an AND circuit 4 the output of which is applied via cathode follower stage 3 to the power stage 2 and in which a selective negative feedback circuit between the cathode of tube 2 and the grid circuit of tube 3 restricts the voltage rise on the grid of tube 3 when the amplitude of the current pulse in tube 2 has reached a predetermined level. The negative feedback circuit may be common to other cathode follower and power stages which are connected respectively to terminals 16, 11. When a current pulse is delivered by tube 2 a positive pulse of the same shape appears at the anode of tube 12 the negative peak in the rising portion of the pulse being clamped by a diode circuit 13. Triode 12<SP>1</SP> functions as an impedance transformer for the feedback circuit and as a cathode follower a capacitor 14 constituting a partial negative feedback loop to stabilize the amplifying stage and improve its response. The output of tube 12<SP>1</SP> is applied to double triode stage 15 and thus to the AND gate 4. The bias of tube 12<SP>1</SP> is set by potentiometer 17 and determines the current pulse level below which negative feedback does not appear. Appreciable change in amplitude of the current pulse due to temperature change in the array 1 may be automatically compensated by a thermistor in the circuit. Inductor 10 balances the action due to distributed capacity between the electrodes on tubes 12. In a modification Fig. 2, (not shown) the array 1 is fed in shunt via a capacitor from the anode of tube 2. Or the array may constitute the cathode load of the tube 2, Fig. 3, (not shown). If the array is to be supplied with alternative positive and negative pulses two generators can be associated Figs. 4 and 5 (not shown). Fig. 6 shows the negative feedback circuit for two groups of generators delivering different current pulses which are not simultaneous. Each circuit 8A, 9A, 10A &c. is calculated so that the currents 1A, 1B produce or the cathode of tube 12 a negative feedback signal of the same amplitude. Fig. 7 shows a transistor circuit for producing a current pulse in a magnetic array 1 e.g. a ferrite array. Timing and selecting pulses applied to the terminals 5, 6 of an AND gate 4 are amplified by the emitter follower stage 3 and applied to stage 2. The voltage at terminal 11 which is proportional to the current flow through array 1 is applied to the base of transistor 21 and thus via gate 4 to the base of transistor 3 thus constituting a negative feedback circuit between transistors 2, 3. The bias voltage at terminal 22 for the emitter of transistor 21 is maintained strictly constant, for example from a tapping on a potentiometer across the D.C. supply source, since it defines the level of current pulse in array 1 below which negative feedback is not operative. By this means current pulses are induced in array 1 having an amplitude which is limited above a predetermined level by the action of the negative feedback circuit via transistor 21. A common negative feedback circuit may be used to connect a number of AND gates to a number of output transistors 2. PNP type transistors may be used instead of NPN.