Method and apparatus for sensing tunnel magneto-resistance

An apparatus, comprising:

• a first MRAM (magnetic random access memory) cell array, comprising:
• a first reference cell controlled by a first control signal;
• a first calibration cell;
• and
• a first set of data cells;
• a second MRAM cell array comprising:
• a second reference cell controlled by a second control signal;
• a second calibration cell;
• and
• a second set of data cells;
• and
• a sensing-amplifier/latch, for detecting a difference between the first reference cell and the second calibration cell to generate the first control signal in a first calibration process and detecting a difference between the second reference cell and the first calibration cell to generate the second control signal in a second calibration process;
• wherein during a read operation for a selected data cell among the first set of data cells, a state of the selected data cell is detected by sensing a difference between the selected data cell and the second reference cell, and during a read operation for a selected data cell among the second set of data cells, a state of the selected data cell is detected by sensing a difference between the selected data cell and the first reference cell.

A method, comprising:

• incorporating a calibration MRAM cell into a MRAM cell array;
• presetting the calibration MRAM cell to a first state;
• incorporating a reference MRAM cell controlled by a control signal;
• presetting the reference MRAM cell to a second state;
• presetting the reference control signal to a first value such that a resistance of the reference MRAM cell is equal to a resistance of the calibration MRAM cell if the calibration MRAM cell were preset in the second state;
• gradually adjusting the control signal until it reaches a second value where the resistance of the reference MRAM cell is equal to the resistance of the calibration MRAM that has been preset to the first state;
• choosing a mean value between the first value and second value as a calibrated value for the control signal;
• and
• using the reference MRAM cell with the calibrated value for the control signal as a reference for detecting a state of a MRAM cell selected within the MRAM cell array when a read operation is performed.