Patent GB-1042024-A (GB)
Title: Improvements relating to analogue signal storage devices
Inventor: FRANKLIN DONALD PETER
IPC: G11C27/02
Filed: 1962-05-23
Abstract: 1,042,024. Controlled non-linear inductors; transistor circuits. ELECTRIC & MUSICAL INDUSTRIES Ltd. May 23, 1963 [May 23. 1962], No. 19751/62. Headings H3B and H3T. In an analogue signal storage device in which a magnetic structure has a main magnetic circuit and a minor magnetic circuit, the main magnetic circuit is magnetized below saturation to an extent dependent on the strength of an input signal so storing an analogue of the signal and an alternating flux change is induced in the minor magnetic circuit so as to saturate the latter alternately in opposite directions resulting in an output signal representing the stored analogue being induced in an output winding. As shown in Fig. 1, a ferrite magnetic structure 1 comprises three limbs 2, 3, 4 which together form the main magnetic circuit, the minor magnetic circuit comprising limbs 2, 3. Winding 5 is connected to signal voltage source 8 by way of switch 27, Fig. 3, which is operated by sampling pulses so that source 8 is connected to winding 5 for a precise period, and is also connected to the negative supply through switch 29. Initially switch 29 is closed so that heavy current passes through winding 5 to leave the limbs 2, 3 saturated. Voltage source 8 is now connected to the winding 5 for a predetermined length of time by operating switch 29 such that the flux in limb 4 is reduced by an amount #x proportional to the volts-time integral of the winding 5. Since limb 4 behaves as a permanent magnet providing a substantial constant flux the amplitude of possible flux variations in the limbs 2, 3 is #x representative of the volts-time integral applied from source 8. An alternating flux variation in the limbs 2, 3 for deriving an output signal representing the stored analogue is produced by the free running multivibrator comprising transistors 9, 10 having their collector and bases cross-coupled as shown, diodes 15, 16 being provided to limit the emitter current of the transistors 9, 10 when the flux in the limbs 2, 3 is charging and on which are wound windings 6, 7 connected between the collectors of the transistors and the negative supply. The inverse frequency modulated square wave sot up in the multivibrator is picked up by a winding 17 associated with the magnetic structure 1, and the voltage after being amplified and clipped in 18, 19 is integrated by 20, 21, 23, 24, 25 and fed through filter 26 which removes the frequency of the multivibrator from the integrated waveform and gives a steady voltage proportional to the flux #x which is proportional to the voltage signal applied from source 8. The switch 27 may take the form shown in Fig. 3 in which voltage source 8 is connected to winding 5 through the emittercollector path of transistor 29 rendered conducting under the control of pulses applied to its base by monostable multivibrator 36. This latter transistor is pulsed into conduction by pulses applied through capacitor 37 and saturates due to feedback over windings 32, 33 until saturable core 30 is saturated, when the transistor 36 is again cut off. An alternative form of switch 27, Fig. 4 (not shown), comprises an inductor and capacitor connected in parallel across an earth terminal and a source of constant current, the pulses for switching, the transistor 39 of Fig. 3 being taken from across. the inductor.