Patent GB-1199381-A (GB)
Title: Data Storage Apparatus.
Inventor: GILLETT JOHN BRIAN
IPC: G11C7/00
Filed: 1968-05-02
Abstract: 1,199,381. Magnetic storage arrangements. INTERNATIONAL BUSINESS MACHINES CORP. 2 May, 1968, No. 20766/68. Heading H3B. To non-destructively read out an anisotropic thin magnetic film storage element 13, Fig. 1, an A.C. of frequency f is applied to a word line 12 so that an A.C. of frequency 2f is induced in a bit line 11 having one of two possible phase positions depending on the digit stored, the capacitive coupled noise which is also developed in the bit line being used as a source of strobe signals to determine the identity of the digit read out. In the storage matrix 10 shown, a decoding tree 15, controlled from word select lines 16 through amplifiers 17, applies A.C. of frequency f to a selected word line 12 for both reading and writing. Further decoding trees 19, each provided for a different group of bit lines 11, are controlled by segment select lines 24 through amplifiers 23, and are effective to connect a selected bit line in a group to a bit driver 20 and a sense amplifier 21. For writing, word and bit drivers 14 and 20 are operative simultaneously, and apply A.C. of frequency f and 2f respectively to a selected storage element in a group, the phase position of the A.C. of frequency 2f from bit driver 20 determining the stable state along the easy axis of magnetization to be established in the storage element. For reading out from a selected element in a group, the appropriate bit line is coupled by the associated decoding tree 19 to the sense amplifier 21, the A.C. of frequency f from the word driver inducing A.C. of frequency 2f in the bit lines. In addition, each bit line of the group picks up capacitive noise of frequency f. The decoding tree passes the A.C. of frequency 2f in the bit line of the selected storage element to the sense amplifier and passes the capacitive noise in all the bit lines of the group to this amplifier. The phase position of the A.C. of frequency 2f is determined by the binary digit stored in the interrogated storage element, and the identity of the digit is determined by the sense amplifier circuit shown in Fig. 4 in which the frequencies f and 2f are segregated by bandpass filters 31 and 32, respectively. The capacitive noise through filter 31 generates strobe pulses of frequency 2f in a strobe 33, the strobe circuit being responsive to each zero of the capacitive noise of frequency f. The strobe pulses control a gate 35, and thus enable the phase position of the A.C. of frequency 2f from the interrogated storage element to be determined by an integrator 36 and threshold switch 37. The decoding trees, Fig. 3, each comprise a branching arrangement of parallel L-C circuits, each circuit being represented in the Figure by a square box. The inductor L of each L-C circuit has an associated control line A, #A ... C, and is saturated when its control line is D.C. energized. Each L-C circuit in the decoding tree 14 is resonant at frequency f when unsaturated, and in each decoding tree 19 is resonant at frequency 2f. Thus the associated word or bit driver is operatively connected to the required line by saturating selected L-C circuits in a decoding tree. In the case of the decoding trees 19, since the parallel L-C circuits connected to unselected bit lines have a high impedance at the resonant frequency 2f, but not at frequency f, the capacitive noise in each of the bit lines of a group is able to pass through the decoding tree and therefore act cumulatively in the sense amplifier.