Method of detecting changes in integrated circuits using thermally imaged test patterns

A method of testing an electrical circuit, comprising:

• selecting test vectors for electrically activating portions of a first electrical circuit of a preselected design over time;
• generating a set of expected results including information on expected activity corresponding to expected thermal changes of portions of the first electrical circuit expected to be activated by application of the test vectors, times over which the portions are expected to be activated, and expected output signals associated with application of the test vectors;
• applying the test vectors to a second electrical circuit of the preselected design and generating output signals of the second electrical circuit corresponding to the test vectors;
• detecting activated portions of the second electrical circuit over time by identifying thermal changes in the second electrical circuit during application of the test vectors;
• comparing the output signals of the second electrical circuit with the expected output signals;
• and
• comparing a plurality of images based on the thermal changes of the second electrical circuit over time with the expected thermal changes, wherein when the second electrical circuit generates output signals matching the expected output signals, the comparison of thermal changes identifies unexpected internal activity in the second electrical circuit originating from circuitry different from circuitry associated with the preselected design that do not change or affect the generated output signals.