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.

Output-bit selection is a recently proposed test-response compaction approach that can effectively deal with aliasing, unknown-value, and low-diagnosis problems. This approach has been implemented using a single counter and a multiplexer without considering unknown values. Also, such an implementation may require the application of a pattern multiple times in order to observe all selected responses. In this paper, we present a multiple-counter-based architecture with a new selection algorithm that can avoid most unknown-values yet achieve high compaction ratio. The remaining small number of unknowns can then be dealt with using some simple masking logic. Experiments on IWLS'05 circuits show that even with 16% unknown responses, all unknown values can be handled with 88.92%~93.21% response-volume reduction still achieved and only a moderate increase in test-application time.

This paper proposes an efficient diagnosis-aware ATPG method that can quickly identify equivalent-fault pairs and generate diagnosis patterns for nonequivalent-fault pairs, where an (non)equivalent-fault pair contains two stuck-at faults that are (not) equivalent. A novel fault injection method is developed which allows one to embed all fault pairs undistinguished by the conventional test patterns into a circuit model with only one copy of the original circuit. Each pair of faults to be processed is transformed to a stuck-at fault and all fault pairs can be dealt with by invoking an ordinary ATPG tool for stuck-at faults just once. High efficiency of diagnosis pattern generation can be achieved due to 1) the circuit to be processed is read only once, 2) the data structure for ATPG process is constructed only once, 3) multiple fault pairs can be processed at a time, and 4) only one copy of the original circuit is needed. Experimental results show that this is the first reported work that can achieve 100% diagnosis resolutions for all ISCAS'89 and IWLS'05 benchmark circuits using an ordinary ATPG tool. Furthermore, we also find that the total number of patterns required to deal with all fault pairs in our method is smaller than that of the current state-of-the-art work.

During an at-speed scan-based test, excessive capture power may cause significant current demand, resulting in the IR-drop problem and unnecessary yield loss. Many methods address this problem by reducing the switching activities of power-risky patterns. These methods may not be efficient when the number of power-risky patterns is large or when some of the patterns require extremely high power. In this paper, we propose discarding all power-risky patterns and starting with power-safe patterns only. Our test generation procedure includes two processes, namely, test pattern refinement and low-power test pattern regeneration. The first process is used to refine the power-safe patterns to detect faults originally detected only by power-risky patterns. If some faults are still undetected after this process, the second process is applied to generate new power-safe patterns to detect these faults. The patterns obtained using the proposed procedure are guaranteed to be power-safe for the given power constraints. To the best of our knowledge, this is the first method that refines only the power-safe patterns to address the capture power problem. Experimental results on ISCAS'89 and ITC'99 benchmark circuits show that an average of 75% of faults originally detected only by power-risky patterns can be detected by refining power-safe patterns and that most of the remaining faults can be detected by the low-power test generation process. Furthermore, the required test data volume can be reduced by 12.76% on average with little or no fault coverage loss.

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.

Twisted-ring-counters (TRCs) have been used as built-in test pattern generators for high-performance circuits due to their small area overhead, low performance impact and simple control circuitry. However, previous work based on a single, fixed-order TRC often requires long test time to achieve high fault coverage and large storage space to store required control data and TRC seeds. In this paper, a novel programmable multiple-TRC-based on-chip test generation scheme is proposed to minimize both the required test time and test data volume. The scan path of a circuit under test is divided into multiple equal-length scan segments, each converted to a small-size TRC controlled by a programmable control logic unit. An efficient algorithm to determine the required seeds and the control vectors is developed. Experimental results on ISCAS'89, ITC'99 and IWLS'05 benchmark circuits show that, on average, the proposed scheme using only a single programmable TRC design can achieve 35.58%-98.73% reductions on the number of test application cycles with smaller storage data volume compared with previous work. When using more programmable TRC designs, 83.60%-99.59% reductions can be achieved with only slight increase on test data volume.

Output selection is a recently proposed test response compaction method, where only a subset of output response bits is selected for observation. It can achieve zero aliasing, full X-tolerance, and high diagnosability. One critical issue for output selection is how to implement the selection hardware. In this paper, we present a counter-based output selection scheme that employs only a counter and a multiplexer, hence involving very small area overhead and simple test control. The proposed scheme is ATPG-independent and thus can easily be incorporated into a typical design flow. Two efficient output selection algorithms are presented to determine the desired output responses, one using a single counter operation for simpler test control and the other using more counter operations for achieving a better test-response reduction ratio. Experimental results show that for stuck-at faults in large ISCAS'89 and ITC'99 benchmark circuits, 48%~90% reduction ratios on test responses can be achieved with only one counter and one multiplexer employed. Even better results, i.e., 76%~95% reductions, can be obtained for transition faults. It is also shown that the diagnostic resolution of this method is almost the same as that achieved by observing all output responses.

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.

Output selection is a recently proposed test response compaction method, where only a subset of output response bits is selected for observation. It can achieve zero aliasing, full X-tolerance, and high diagnosability. We propose an output selection scheme for multiple scan designs, which employs only accumulators and multiplexers, and thus involves small area overhead and simple test control. An efficient selection procedure is presented to determine a minimal test set and the corresponding output bits to select for complete fault coverage. Experimental results show that when only one accumulator and one multiplexer are employed, 100% single stuck-at fault coverage for ISCAS'89 (ITC'99) circuits can be achieved by observing only 9.84% (8.19%) of the test response bits with only 1.86% (1.18%) area overhead.

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.

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.