Patent GB-1287102-A (GB)
Title: Analogue storage device
Inventor: UNDERHILL MICHAEL JAMES
IPC: G11C27/00
Filed: 1968-12-31
Abstract: 1287102 Analogue storage apparatus MULLARDLtd 3 Sept 1969 [31 Dec 1968] 61956/68 Heading H3B [Also in Division G1] In an analogue storage arrangement, in which the magnetization intensity of a remanent magnetic body is a measure of the stored information, read out is performed by observing polarization plane changes in an electromagnetic radiation beam passed through a transparent and magneto-optic portion of the body. A YIG core 1, Fig. 1, is initially saturated by a current in coil 2 and then part of the flux is switched by an input signal applied to coil 2 or a second coil. Infra-red radiation from source 3 is passed through plane polarizer 5, body 1, analyser 6 to a photodetector 7 whereby the plane of polarization is rotated by the state of core 1 so that the amount of radiation falling on photodetector 7 is a measure of the amplitude of the input signal. The core 1 may be in the form of a single crystal, Fig. 1b (not shown) or in two parts one semicircular, Fig. lc (not shown), or D-shaped, Fig. 1d (not shown). A matrix of analogue storage elements may be provided by a sheet of Y1G having a matrix of holes through which pairs of coordinate input conductors are passed, Fig. 2 (not shown). In an alternative method of operation to that described in Fig. 1(a) the state of magnetization of the core 1 is continuously read during storing, the storing process ceasing when the output from the photodetector reaches a predetermined value. A rod of magneto-optic non-remanent material provided with a coil may be inserted between the plane polarizer 5 and core 1, Fig. 3a (not shown). The input signal to be stored is applied to the coil on the rod to rotate the plane of polarization of the radiation. Flux is then switched into the core to rotate the plane of polarization until the output from the photodetector is the same as that occurred with no input signal. To read out a current is passed through the coil on the rod until it rotates the light beam by an equal and apposite amount to that of the core so that the output from the photodetector is the same as that which occurred when no information was stored. The non- remanent rod may be used in parallel with the remanent core, Fig. 3b (not shown), in which case two matched photodiodes may be used. Fig. 3c shows a track and hold store in which in the absence of an input signal at 46 only a 20 KHz signal is applied to non-remanent rod 20 so that the light beam is incident on the analyser 6 at 90 degrees resulting in a zero component at 20 KHz in the output from photodetector 7. A varying input signal to be tracked is applied to coil 211 and contact 45 moved into the position shown. The resultant polarization plane rotation produces a 20 KHz component in the output from 7 the magnitude and phase of which depends on the magnitude and direction of the rotation, and is converted to a control voltage level by detector 42 which is applied to pulse generator 43. Variable amplitude pulses are applied to coil 2 to change the state of core 1 so that the output from 7 is again zero when contacts 44, 45 are moved to the hold position. When the light beam is again passed through the apparatus it is rotated by core 1 so that the resultant output from detector 42 passes through coil 211 to bring the output to the null position again, the output voltage necessary to achieve this being measured at terminal 47.