A MAGNETIC FILM MEMORY

1,249,377. Magnetic storage apparatus; digital transmission systems. INTERNATIONAL BUSINESS MACHINES CORP. 11 Sept., 1969, No. 44809/69. Addition to 1,199,382. Headings H3B and H4P. An anisotropic thin film memory in which read out of information is effected using oscillatory drive signals and stored information is detected from the phase of the read out signals as described in the parent Specification, is modified by the inclusion of two phase lines. The n+2xN array 10 of anisotropic film elements includes n-bit lines 12 and two phase lines 13, 14, all the magnetic elements associated with one phase line being magnetized in the same direction along the easy axis parallel to word lines 11 and all the elements associated with the other phase line being magnetized in the opposite direction along the easy axis. During a read operation an oscillatory signal of frequency f in the range 10 to 100 MHz is applied to a selected word line 11 so that each magnetic element in the selected word line 11 1 has its magnetization vector oscillated to induce signals of frequency 2f in each of the bit lines 12 and the two phase lines 13, 14, the phase of the signal developed on each line being characteristic of the information stored in the element coupled thereto and are 180 degrees out of phase with each other for binary zero and one. The signal generated on a bit line 12 selected by bit select gate 19 is separately correlated with the two out-of-phase signals generated on the lines 23, 24 at 25, 26 to produce an integral with respect to time of the multiple of the respective voltages of the two signals applied to the respective correlation circuit 25, 26. The outputs from the circuits 25, 26, i.e. positive or negative dependent upon whether the signal from the bit line is in phase or out of phase with the phase line signals, are applied to differential amplifier 29 which produces an output at 22 of one polarity or the other dependent upon the nature of the stored information. The arrangement cancels capacitive noise signals and attenuates random thermal noise signals. Detection circuit, Fig. 2. The bit signal from the selected bit line is applied to terminal 30 and the reference phase signals to terminals 31, 32 respectively. The resultant current flow in transistors T2, T3 is in a ratio depending on the voltage difference between the phase signals supplied to their respective base electrodes and capacitor 34 is charged accordingly. After a predetermined time the charge o