Method and apparatus for initializing reference cells of a toggle switched MRAM device

A method of initializing a reference cell in a toggle switched MRAM device, the method comprising:

• performing a first read operation of the reference cell by comparing current through the reference cell with the average current passing through a pair of data cells, and storing the result of the first read operation;
• inverting the value of one of the pair of the data cells;
• performing a second read operation of the reference cell, and storing the result of the second read operation;
• inverting the value of the other of the pair of the data cells;
• performing a third read operation of the reference cell, and storing the result of the third read operation;
• performing a majority compare operation of the results of the first, second and third operations, wherein the result of the majority compare operation is the initial state of the reference cell and
• toggling the reference cell in the event the initial state of the reference cell does not match a desired state of the reference cell.

An apparatus for initializing a reference cell in a toggle switched MRAM device, the apparatus comprising:

• a first sense amplifier configured for performing a first read operation of the reference cell by comparing current through the reference cell with the average current passing through a pair of data cells;
• a first latch for storing the result of the first read operation;
• a second latch for storing the result of a second read operation by the first sense amplifier, wherein the second read operation is performed following the first read operation and the inversion of the value of one of the pair of the data cells;
• a third latch for storing the result of a third read operation by the first sense amplifier, wherein the third read operation is performed following the second read operation and the inversion of the value of the other of the pair of the data cells;
• and a majority compare device configured to compare the results of the first, second and third operations respectively stored in the first, second and third latches, wherein an output of the majority compare operation is the initial state of the reference cell.