Patent ID: 7882455

Claim:
A circuit comprising: a semiconductor chip; a plurality of phase change elements on said semiconductor chip, all of said phase change elements being programmed to an amorphous state so as to have approximately equal amorphous resistances and so as to exhibit essentially the same temperature-dependent electrical properties; a comparator circuit on said semiconductor chip, said comparator circuit comprising: a first current source generating a first current and being electrically connected to a selected phase change element through a switching circuit, said selected phase change element being located at a first location on said semiconductor chip; a second current source generating a second current and being electrically connected to a reference phase change element, said reference phase change element being different from said selected phase change element and being located at a second location on said chip; and a voltage difference detection device comprising: a first input electrically connected to a first node between said first current source and said selected phase change element; and a second input electrically connected to a second node between said second current source and said reference phase change element, said voltage difference detection device comparing a first voltage at said first input and a second voltage at said second input to detect a voltage difference between said first voltage and said second voltage, said voltage difference being indicative of a temperature difference between said first location and said second location.