Self referencing sense amplifier for spin torque MRAM

摘要

Circuitry and a method provide self-referenced sensing of a resistive memory cell by using its characteristic of resistance variation with applied voltage in one state versus a relatively constant resistance regardless of the applied voltage in its opposite state. Based on an initial bias state with equalized resistances, a current comparison at a second bias state between a mock bit line and a bit line is used to determine the state of the memory cell, since a significant difference in current implies that the memory cell state has a significant voltage coefficient of resistance. An offset current applied to the mock bit line optionally may be used to provide symmetry and greater sensing margin.

主权项

1. A method of reading data from a spin-torque magnetoresistive memory cell coupled to a bit line, the memory cell having resistance variation with applied voltage in a first state, and the memory cell having relatively constant resistance regardless of applied voltage in a second state, the method comprising:
biasing a transistor to operate in a linear region, wherein the transistor is coupled to a mock bit line; providing a first applied voltage to the bit line and to the mock bit line; while the first applied voltage is provided, adjusting a gate voltage of the transistor such that resistance of the transistor matches resistance of the memory cell; after adjusting the gate voltage, providing a second applied voltage to the bit line and to the mock bit line; comparing a current difference between the bit line with the second applied voltage and the mock bit line with the second applied voltage; and determining whether the memory cell is in the first state or the second state in response to the comparison of the current difference.