MAGNETIC THIN FILM MEMORY

1,214,024. Circuits employing bi-stable magnetic elements. INTERNATIONAL BUSINESS MACHINES CORP. 6 Aug., 1968, No. 37412/68. Heading H3B. In a magnetic thin film memory information is read out of a word by applying an oscillatory active signal of frequency # together with a biasing magnetic field to the elements of a word and detecting the phase of signals at frequency # produced in the associated bit lines. The memory of Fig. 2 comprises in groups 10a, 10b to 10m each of which is an N x n array of anisotropic thin films and includes n bit lines 11 each extending along a respective row of elements and a single bias line 12 extending along all the columns of elements in the group for simultaneously applying a hard axis bias field. To effect read out of data from a word storage location an oscillatory drive signal is supplied by word drive circuit 14 to the word line coupled to the required word storage location and a bias signal applied simultaneously to the bias line 12 of the group in which the required storage location is located. A sense signal is developed in all of the sense/bit lines 11 of the memory but only the bit lines of the group to which the bias current is applied have a significant component at the fundamental frequency # of the sinusoidal drive signal. The signals at the fundamental frequency are passed by filters 23 to phase detectors 24 and the signals developed on output lines 25 are indicative of the data stored, Fig. 3 (not shown). Information is stored by applying bit currents to selected bit/sense lines of the required polarity simultaneously with the oscillatory word drive signal and bias field applied to a selected word line, Fig. 4. As shown all the diodes 27 of each segment are connected to a respective control line 29 and all diodes 28 are connected to control line 30. In order to select the bit lines of a respective group for the storage of information control lines 29, 30 are both connected to ground potential, control lines 29, 30 of unselected segments being connected to negative and positive potentials respectively. Resistors 31 and capacitors 32 present an open circuit to the bit currents but provide a resonable termination at the high frequencies of the sense signals during reacting. The oscillatory drive signals may be applied to the bias lines and the D.C. bias signal applied to the word lines. The hard axis bias field may be provided by field windings or coils surrounding respective segments of the memory instead of a