Patent GB-804796-A (GB)
Title: Improvements in or relating to electrical pulse generation
Inventor: BEAUFOY RAYMOND
IPC: G11B20/16
Filed: 1954-09-01
Abstract: 804,796. Electric digital data-storage apparatus. BRITISH TELECOMMUNICATIONS RESEARCH Ltd. Aug. 30, 1955 [Sept. 1, 1954], No. 25426/54. Class 106 (1). [Also in Group XXXIX] In a multivibrator producing strobe pulses from which are derived reference pulses for positions on a magnetic drum, the strobe pulses are compared in phase with a sine wave received from the magnetic drum in a comparison circuit whose output controls the period of the multivibrator. As shown, Fig. 1, valves VT2, VT3 constitute an asymmetric multivibrator producing short pulses on lead 10 for controlling reading and writing on the drum. During the pulse lead 10 becomes positive with respect to lead 11, thereby opening the gate MR1 . . . MR4 to admit from lead 12 the sine wave from the drum to condenser C1 which stores the signal so received and feeds it to the grid of VT1 and according as the sine wave is at a positive or negative point at the instant of the pulse VT1 increases or decreases the bias potential or the grid of VT2 to increase or decrease the frequency of the multivibrator. The condenser C1 may be made large to smooth out minor variations in the received frequency due, e.g., to drum " jitter." An anti-hunting device may be included in the circuit if necessary. As described, the invention is applied to a system of the type described in Specification 717,690, [Group XXXIX], in which each recording track is divided into 20 groups, each of 14 blocks, each of which contains six units in which a binary digit can be registered. Pulses for determining the units positions are obtained by feeding the strobe pulses over lead 15, Fig. 3, to a ring of three bistable state devices M1, M2, M3, each of which opens a gate for the succeeding device. Thus with M1 switched to its " upper " state it open the upper rectifier gate to permit the next strobe pulse to switch M2 to its " upper " state. Similarly the next strobe pulse switches M3 to its " upper " state. M3 then opens a gate to permit the next strobe pulse to switch M1 to its " lower " state and similarly M2 and M3 follow to the next strobe pulses after which the circuits go successively to their upper states and so on. Thus each of the circuits M1, M2, M3 switches from one state to another after a period corresponding to three units positions the times of switching being staggered. The outputs from these circuits are appropriately combined in gating circuits to produce outputs corresponding to any one of the six units positions or combinations thereof as required, Fig. 4 (not shown). In order to remedy the possible setting up on starting of an undesirable pattern (e.g. opposite tubes conducting in adjacent bi-stable devices) a further coincidence circuit is introduced for the input of M3 which ensures that M3 cannot operate until both M1 and M2 are in their " upper " phases. A similar circuit comprising 7 bi-stable circuits and fed by strobe pulses gated by the last of the units pulses is used to obtain " block " pulses and a further circuit comprising 10 bi-stable circuits is used for obtaining " group " pulses. There is also described means for relating the track positions to a reference position on the drum. In the reference position the period of the sinusoidal wave is doubled so that the phase thereof changes momentarily as shown in Fig. 5. A bistable circuit of the type described in Specification 804,071 detects this change and produces positive and negative outputs SLc, SLc, Fig. 6. Leads TX6, TY14 and TZ20 all carry negative signals when the drum should be in the position corresponding to the last units position of the last block of the last group, this position being intended to correspond with the reference position on the sine wave. When a drum is started up the first SLc pulse triggers the circuit MC to open a rectifier gate to permit strobe pulses from lead 22 to pass via lead 15 to the ring counting circuits. These are stepped until they emit negative signals on leads TX6, TY14, TZ20. If due to lack of synchronism the SLc pulse has not yet arrived the lead SLc will also be at negative potential so that a negative signal is applied to restore the trigger circuit MC, thereby cutting off the supply of strobe pulses from lead 15. When the SLc pulse occurs again MC is again triggered and the strobe pulses recommence the stepping of the ring circuits which are now synchronized relative to the reference position on the drum. The circuit of Fig. 6 is the subject of the claims of divided Specification 804,797, [Group XXXIX]. Specification 801,681 also is referred to.