Patent ID: 7486546

Claim:
A multi-state sense amplifier, coupled to at least one memory cell with changeable resistance and a plurality of reference cells, comprising: a first current mirror circuit, coupled to the output terminal of the memory cell, generating a second memory cell current at a first node according to a first memory cell current through the memory cell; a second current mirror circuit, coupled to the output terminal of the reference cells, generating a plurality of second reference currents at a plurality of second nodes according to a plurality of first reference currents through the reference cells; and a load circuit, coupled to the first node, the second nodes, and a ground, providing equal loads for the second memory cell current and the second reference currents to respectively generate a memory cell voltage at the first node and a plurality of reference voltage at the second nodes; wherein the level of the second memory cell current is twice the level of the first memory cell current, the levels of the second reference currents are the same as the levels of the first reference currents, and the ratios of the memory cell voltage to the reference voltages are equal to the ratios of the second memory cell current to the reference currents.