Patent GB-827855-A (GB)
Title: Marker pulse timing circuit
IPC: G06F1/04
Filed: 1956-03-02
Abstract: 827,855. Automatic waveform control systems. INTERNATIONAL BUSINESS MACHINES CORPORATION. March 2, 1956 [March 7, 1955], No. 6601/56. Class 38 (4). [Also in Group XL (c)] In a pulse train the pulse repetition frequency of which may vary a second train of pulses is slotted in between each of the pulses in such a position that the time delay between a pulse of the first train and the slotted pulse is a predetermined and fixed ratio of the time period between pulses of the first train. The first pulse train, the frequency of which may vary, is applied to a mono-stable multivibrator circuit which has a controllable duty cycle the output from the multivibrator being applied via integrating circuits to produce a D.C. control voltage which is fed back to the multivibrator so that even when the repetition frequency of the input pulse train varies the duty cycle of the pulses generated by the multivibrator remains constant. Fig. 1 shows the application to a magnetic drum recording device 10 in which the clock pulses read off by head 11 may vary in frequency due to changes in the speed of rotation of the drum. The pulses W14, Fig. 1A, are passed via amplifier 12 to a compensating pulse generator 15 the output of which W16, Fig. 1A, is a pulse train, the duty cycle of which is maintained constant irrespective of changes in the repetition frequency of the train W14. The output of the generator 15 is differentiated by circuits 18, 18a and clipped and inverted so that a train of positive pulses W23 is produced at output 23, each of which is delayed by a constant time ta after pulses of the train W14. The output from differentiator 18 is also applied to a fullwave rectifier 20 to produce a train of positive pulses W21 having a repetition frequency twice that of the input train W14. The pulses W21 may be used as a clock pulses for circuits required to be synchronized with magnetic drum 10 and the pulses W23 as clock pulses for part of a computer which are required to operate at a frequency which is a multiple of that of the synchronizing pulses derived from drum 10. As shown in Fig. 2A, the positive input pulse train W14, Fig. 1A, is applied via phase inverter tube 33 to a mono-stable multivibrator circuit comprising tubes 45, 47 in which tube 45 is normally cut-off and tube 47 conducting. The pulse repetition frequency of the output pulses derived from the anode of tube 47 is determined by the setting of potentiometer 55 and the changeover point of the multivibrator by the bias at the control grid of tube 45 thus the ratio of ta/(ta+tb), Fig. 1A, may be adjusted by alteration of the bias at the grid of tube 45. The output pulses from the flipflop 45, 47 which are available at terminal 16 are phase split in tube 67 clamped by divider 77, 87 and integrated by circuits 79, 82 and 89, 92, the average D.C. voltages thus being derived are applied respectively to the tubes 81, 91 of a differential amplifier which operates so that the change in the voltage at anode 91 i.e. on lead 61 is proportional to the difference between the D.C. voltages at the grids of tubes 81, 91. Potentiamater 96 is adjusted so that there is a voltage V at anode 91 when equal grid volts are applied to the amplifier i.e. when the duty cycle of the pulse train on terminal 16 is 50%. This voltage V is adjusted to be equal to that available at switch 60 when it is in its OFF position thus establishing a reference level. If due to a change in the repetition frequency of the pulses applied a terminal 14 and thus that of multivibrator 45, 47 the duty cycle of the pulse train at terminal 16 changes the average D.C. voltages applied to the grids of tubes 81, 91 produce a resultant voltage on lead 61 which differs from the reference voltage, this being applied to tube 45 to control the change-over point of multivibrator 45, 47 and to adjust the duty cycle back to the predetermined value. Fig. 2B shows a phase-splitter stage 103 and full-wave rectifiers 109, 110 which produce from an input pulse train 116 an output train of positive pulses 119 having twice the repetition frequency of that applied at terminal 16. The pulses 116 are also applied to a differentiating circuit 122, 123 and clipper inverter stage 124, 125 to produce a train of output pulses having the same repetition frequency as the input pulse train but each being delayed by a predetermined period after each pulse of the input train. In the modification shown in Fig. 7 which is associated with Fig. 2B, the pulse train generated at output 16 is applied via tube 160 to charge capacitors 168, 174 via rectifiers 164, 165 respectively, the algebraic sum of the D.C. voltages produced, across capacitors 168, 174 is applied to the grid of tube 171 of differential amplifier 171, 178. The output on lead 61 is a control voltage having a predetermined D.C. value when the duty cycle of the monostable multivibrator 47, 45 is at a predetermined value controlled by the voltage applied to the grid of tube 45. The potentiometer 161 is adjusted in dependence upon the duty cycle of the pulse train at terminal 16.