A method and apparatus for selectively masking off unknown (`x`) captured scan data in first selected scan cells 220 from propagating through the scan chains 221 for test, debug, diagnosis, and yield improvement of a scan-based integrated circuit 207 in a selected scan-test mode 232 or selected self-test mode. The scan-based integrated circuit 207 contains a plurality of scan chains 221, a plurality of pattern generators 208, a plurality of pattern compactors 213, with each scan chain 221 comprising multiple scan cells 220, 222 coupled in series. The method and apparatus further includes an output-mask controller 211 and an output-mask network 212 embedded on the scan data input path of second selected scan cells 222, or a set/reset controller controlling selected set/reset inputs of second selected scan cells. A synthesis method is also proposed for synthesizing the output-mask controller 211 and the set/reset controller.
RELATED APPLICATION DATA
This application claims the benefit of U.S. Provisional Application No. 60/484,639 filed Jul. 7, 2003, titled "Mask Network Design for Scan-Based Integrated Circuits", which is hereby incorporated by reference.
An apparatus for testing an integrated circuit is disclosed. The apparatus includes a compactor to compress test responses from a circuit under test that is part of an integrated circuit.
The present invention provides a system and method for implementing postponed quasi-masking test output compression in an integrated circuit. The system includes a compressor for compressing a test response from N scan chains of an integrated circuit into M outputs. The test response may indicate faults in the integrated circuit. M and N are positive integers. The system further includes a correctable multiple input signature register with a size of M, which is communicatively coupled to the compressor. The correctable multiple input signature register is suitable for receiving the M outputs from the compressor as data inputs (s[0], . . . , s[M-1]) and receiving M correction bits (c[0], . . . , c[M-1]) and L address bits (a[0], . . . , a[L-1]) as correction inputs, L being a positive integer, 2.sup.L>=M. The correctable multiple input signature register is suitable for detecting faults when there is no or at least one unknown value (i.e., X-value) in the test response.
A spatial compactor design and technique for the compaction of test response data is herein disclosed which advantageously provides a scan-out response with multiple opportunities to be observed on different output channels in one to several scan-shift cycles.
A system, apparatus and method of isolating a plurality of limiting logical cones in a chip during a logical built-in self test (LBIST) are provided. An LBIST is performed on the chip in order to locate a first latch that fails the test. Particularly, latches on the chip are arranged in a plurality of scan chains wherein each latch holds data for a logical cone. The LBIST is performed on one scan chain at a time. Once the first latch is located, a first limiting cone (i.e., the cone for which the first latch is holding data) may be isolated. After isolating the first limiting cone, the data from the first latch is masked out and the LBIST is repeated on the scan chain. The data is masked out in order to facilitate the identification of any other latch that may fail the test. Again, if another latch fails the test a corresponding limiting cone may be isolated.
A compactor has a reduced number of outputs and the ability to handle a higher number of errors and unknown logic values. The procedure for designing the matrix and the resulting compactor involves determining the number of unknown logic values that may be encountered and adding columns to the compactor matrix based on the number of errors. Basically, the number of possible combinations of scan in lines is determined. Then, additional columns are added for each possible combination of scan in lines. The number of columns that are added for each combination of scan in lines is equal to the number of errors plus one in one embodiment.
