Patent GB-1242802-A (GB)
Title: Magnetic film memories
Inventor: VIETH ROBERT FRED
IPC: C04B35/26
Filed: 1969-03-03
Abstract: 1,242,802. Magnetic storage apparatus. LITTON INDUSTRIES Inc. 3 March, 1969 [1 March, 1968], No. 11301/69. Heading H3B. The "waffle iron memory shown in Figs. 1, 2 comprises a ferrite base 10 provided with posts 12 superimposed by low and high coercivity anisotropic thin films 20 and 18 respectively. In the embodiment of Fig. 1 providing a two word, three bits per word memory conductors 24, 26 and 40, 42, 44, 46, 48, 50 carry half write currents, the latter set also acting as sense conductors and word conductors 52, 54 are arranged as shown. In order to write information into the first bit of the first word, the two storage elements of this bit being defined by areas above points 28, 30 in the films 18, 20 coincident current pulses of polarity determined by the bit being stored are applied to conductors 24 and 40, 42, each pulse being of insufficient intensity by itself to rotate the magnetization of film 18 but possibly of sufficient intensity to rotate that of film 20, to rotate the magnetization of both films 18, 20 into one or other direction along the easy axis to store a "1" or a "0". Non-destructive read out is obtained by applying a current pulse to word conductor 52 to generate a field in the hard axis direction which rotates the magnetization of film 20 into the hard axis direction but is of insufficient intensity to rotate that of film 18. The pulse induced in sense conductor 40, 42 is ignored since the direction of magnetization of film 20 may be incorrect due to the effect of half select currents. At the trailing edge of the interrogation pulse the magnetization of film 18 returns to its original position and provides a tipping field for directing the magnetization of film 20 in the opposite direction along the easy axis, the pulse induced in the sense conductors being a true indication of the digit stored. Fig. 2 embodiment.-Information is written into the film 18 by applying coincident current pulses to the appropriate word e.g. 162 line and digit conductor e.g. 164, 166, the polarity of the digit conductor pulse determining whether a "1" or "0" is stored and being of longer duration than the word line pulse to provide a tipping field. Read out is achieved by applying an interrogate pulse to word line 162 of intensity insufficient to rotate the magnetization of film 18 into the hard axis direction but sufficient to rotate that of film 20. As in the first embodiment only that pulse induced in the sense conductor 164, 166 at the trailing edge of the interrogate pulse is utilized. Alternative write of Fig. 2.-The word line current pulse for writing is a two level pulse, Fig. 11 (not shown) the level at the leading edge of the pulse being of sufficient intensity to rotate the magnetization of both films into the hard axis direction. Coincident therewith a tipping pulse is applied to the digit conductor 164, 166 of polarity determining the digit being stored. Before the digit pulse terminates the word pulse drops to its lower level which is insufficient to keep film 18 in the hard axis direction but sufficient to maintain that of film 20 therein. After the digit pulse terminates the word pulse terminates so that the direction of magnetization of film 20 rotates under the control of film into a direction opposite thereto along. Instead of using a step-pulse the word line pulse may be removed in a ramp Fig. 12 (not shown).