Wei Cheng Lien

Test Response Compaction via Output Bit Selection

The conventional output compaction methods based on XOR-networks and/or linear feedback shift registers may suffer from the problems of aliasing, unknown-values, and/or poor diagnosability. In this paper, we present an alternative method called the output-bit-selection method to address the test compaction problem. By observing only a subset of output responses, this method can effectively deal with all the above-mentioned problems. Efficient algorithms that can identify near optimum subsets of output bits to cover all detectable faults in very large circuits are developed. Experimental results show that less than 10% of the output response bits of an already very compact test set are enough to achieve 100% single stuck-at fault coverage for most ISCAS benchmark circuits. Even better results are obtained for ITC 99 benchmark circuits as less than 3% of output bits are enough to cover all stuck-at faults in these circuits. The increase ratio of selected bits to cover other types of faults is shown to be quite small if these faults are taken into account during automatic test pattern generation. Furthermore, the diagnosis resolution of this method is almost the same as that achieved by observing all output response bits.

A Complete Logic BIST Technology with No Storage Requirement

Mixed-mode BIST enhances test efficiency of digital circuits by combining the advantages of both pseudo-random and deterministic patterns. In order to apply the deterministic patterns, most traditional methods need to store some test data in external testers or on-chip memory. In this paper we present a novel mixed-mode BIST technique by which all deterministic patterns can be generated on chip in real time and thus requiring no storage device. By appropriately connecting some internal nets of the circuit under test to the inputs of the circuit, together with a set of pseudo-random patterns, this BIST scheme can reach full fault coverage in a very short time. Experimental results show that all irredundant stuck-at faults in each of the ISCAS85 benchmarks can be detected in less than 1000 test cycles with no storage space required.

A Test-Per-Clock LFSR Reseeding Algorithm for Concurrent Reduction on Test Sequence Length and Test Data Volume

This paper proposes a new test-per-clock BIST method that attempts to minimize the test sequence length and the test data volume simultaneously. An efficient LFSR reseeding algorithm is developed by which each determined seed together with its derived patterns can detect the maximum number of so far undetected faults. During the seed determination process an adaptive X-filling process is first employed to generate a set of candidate patterns for pattern embedding. The process then derives a seed solution that can embed multiple candidate patterns at one time so as to minimize the number of seeds. To shorten the test sequence, the pattern embedding process begins with a small initial set of pseudo-random patterns and will incrementally add more patterns only when necessary. Experimental results show that compared with the previous test-per-clock techniques based on the LFSR- and twisted-ring-counter-reseeding methods, our method can reduce the test sequence length by over 60% with generally smaller numbers of storage bits. When compared with the mapping-logic-based BIST methods, our method can reduce the test sequence length by over 50% with a comparable area overhead.

A rotation-based BIST with self-feedback logic to achieve complete fault coverage

This paper presents a deterministic BIST technique that can efficiently achieve complete fault coverage without using any storage devices. A novel test structure containing a self-feedback logic unit and a circular shift register is proposed by which all the required deterministic patterns can be generated on-chip in real time. Experiments on ISCAS 85 benchmark circuits show that compared with previous work addressing the same problem our technique requires much less test time to achieve 100% fault coverage for all testable stuck-at faults.

A New LFSR Reseeding Scheme via Internal Response Feedback

Reseeding techniques have been adopted in BIST to enhance fault detect ability and shorten test application time for integrated circuits. In order to achieve complete fault coverage, previous reseeding methods often need large storage space to store all required seeds. In this paper, we propose a new LFSR reseeding technique that employs the internal net responses of the circuit itself as the control signals to change the states of the LFSR. A novel test architecture containing a net selection logic module and an LFSR with some inversion logic is presented that can generate all required seeds on-chip in real time without any external or internal storage requirement. Experimental results on ISCAS benchmark circuits show that the presented technique can achieve 100% stuck-at fault coverage in a short test time by using only 0.23-2.36% of internal nets for reseeding control.

Output bit selection methodology for test response compaction

In this paper we propose an output-bit selection technique for test response compaction, with which only a subset of output response bits is selected for observation during testing. Advantages of this technique include zero aliasing, high compaction ratio, full X-tolerance, low area overhead, simple test control and high diagnosability. Also no circuit/ ATPG modification is needed, hence this work can be easily integrated into any typical industrial design/test flow to significantly reduce test cost. Experimental results show that in general less than 10% of test response data of already very compact test sets are needed to detect all testable stuck-at or transition faults, with the reduction ratio increasing with the size of circuits, e.g., only 1.27% of output bits need be observed for b19 that contains more than 1M faults. Efficient test architectures to implement this technique are also presented, which include one that can deal with test responses containing high percentage of unknown values.

A Test-per-cycle BIST architecture with low area overhead and no storage requirement

Test-per-clock BIST scheme has the advantages of very short test application time and small test data volume. However, conventionally this scheme needs an extra parallel response monitor for response analysis that may lead to large area overhead. This paper presents a new test-per-clock BIST method that can perform both pattern generation and response compression concurrently in the same LFSR-based design so as to reduce the area overhead. Furthermore, some internal nets are employed in two ways during test application to help reduce test time and test data volume: 1) as the observation points to enhance fault detectability and 2) as the test data provider for reseeding the LFSR. These two ways lead to the benefits that all required patterns can be generated on chip and at-speed testing can be carried out without using any external or internal storage device. Experimental results show that the presented method can achieve 100% fault coverage in very short time for large ISCAS (IWLS) benchmark circuits using 0.09% (0.03%) of internal nets with 9.29% (8.26%) extra area overhead respectively. When compared with a conventional scan-based design, the area overhead is small considering the features of test-per-clock and no requirement of data storage or expensive test equipment.