Constrained signature-based test

Abstract

A test system for structurally testing an integrated circuit device includes a pattern generator for generating successive random data patterns (scan chain). The test system further includes a constraint checker and corrector module, coupled to the pattern generator, to replace undesirable random data patterns (state elements joined together in the scan chain such that one state element is connected to a ground and the other state element is connected to a power supply) with desirable bit sequences to eliminate bus contention problems in the generated random data patterns. The test system further includes the integrated circuit device to be tested. The integrated circuit device receives the constrained random data patterns from the constraint checker and corrector module and outputs a test result. The test system further includes an X-masking module coupled to the integrated circuit device. The X-masking module receives the test result from the integrated circuit device, and it masks the test result by replacing unpredictable bit values (these are bit values generated due to not scanning some state elements in the scan chain) in the test result with predictable bit values. A signature analyzer coupled to the X-masking module receives the masked test result and compress the test result into a signature. Then a comparator coupled to the signature analyzer compares the signature with a predetermined test result to determine the functionality of the integrated circuit device.