Patent GB-1061919-A (GB)
Title: Thin-film memory with destructive read-out
IPC: G11C11/14
Filed: 1964-11-13
Abstract: 1,061,919. Circuits employing bi-stable magnetic elements. STANDARD TELEPHONES & CABLES Ltd. Nov. 13, 1964 [Nov. 14. 1963], No. 46302/64. Heading H3B. In a destructive read-out magnetic thin film matrix comprising a plurality mn elements of magnetic material exhibiting uniaxial anisotropy arranged in rows and in columns, the sense conductors and one set of drive conductors are arranged parallel to the easy axis of the films. Fig. 4 shows the word Wj in the matrix and comprises thin film elements P1, P2 ... Pn column drive conductors 9.1 . . . 9.n line conductor 10 and sense conductor 11, the directions of the easy and hard directions of magnetization being Hx, Hy. Read and write operations are carried out by selecting the lines 1, 2, 3 ... j . . . m in succession by word time signals T 1  . . . Tj . . . Tm, each being divided into n digit time periods t 1 , t 2  . . . t n  and each digit time period being divided into four basic time periods a, b, c, d. In a read/write cycle a signal Tj is first applied to line current generator 22. j which produces a magnetic field along the hard axis of the film P1 which is in the I state, Figs. 3a, 3b (not shown) and produces a small rotation of the magnetization vector of the film. This rotation together with the direct inductive coupling between 10 and 11 results in a parasitic signal during period a of t 1 , Fig. 5d, but since AND gate 31 is blocked during this period no signal is sent to sense amplifier 32. At time tl.b AND circuit 23 delivers a control signal to read input terminal 6a of generator 21.1 causing a negative read signal, Fig. 5b, to pass down column wire 9À1 and rotate the magnetization vector first from (M2) to (M3), Fig. 3a, and then irreversibly from (M3) to (M4) inducing a signal in the sense conductor 11. At the end of period t 1 .b the field H L  is suppressed and the magnetization vector moves to (M5). During period t 1 Àb AND gate 31 is opened and the induced signals are applied to sense amplifier 32, the output of which sets the bi-stable circuit 33 to its " 1 " state, the output signal 13 being as shown in Fig. 5a. If the information read out is to be written back into the store then during time t1.c signal 13 together with a gating signal are applied to AND gate 34 so that signal 13 is applied to AND gate 26 which is activated at time t1.d. The output from gate 26 activates generator 21.1 so that a writing field +H L  is applied to film P1 rotating the magnetization vector back to position (M2) and so inducing an output signal in sense conductor 11, Fig. 5d. Since AND gate 31 is only activated at the time t1.b the signal does not reach the sense amplifier. The bi-stable circuit 33 is reset to its " 0 " state during each time period " a." During the time t 2  the read/write cycle is applied to film P2 which is in the " 0 " state (M5), Fig. 3a. Since no signal is induced in the sense winding during time period t 2 b bi-stable circuit 33 remains in its " 0 " state and no signal is applied to the re-write signal generator. Fresh information may be read in by applying a signal from S to OR gate 14 during period c. In order to allow for propagation times of signals the word time includes (n + 1 ) digit time period signals t 1  . . . t n , t<SP>1</SP> 0 , the t<SP>1</SP> 0  signal period being used only for rewriting. A multiple-plane parallel memory may also be formed in which case the m sense conductors are connected in series.