A new low-power (LP) scan-based built-in self-test (BIST) technique is proposed based on weighted pseudorandom test pattern generation and reseeding. A new LP scan architecture is proposed, which supports both pseudorandom testing and deterministic BIST. During the pseudorandom testing phase, an LP weighted random test pattern generation scheme is proposed by disabling a part of scan chains. During the deterministic BIST phase, the design-for-testability architecture is modified slightly while the linear-feedback shift register is kept short. In both the cases, only a small number of scan chains are activated in a single cycle. Sufficient experimental results are presented to demonstrate the performance of the proposed LP BIST approach.

Parallelism is one promising solution to accelerating the test pattern generation (TPG) process, several recent works also show that parallel TPG can reduce the test pattern count. However, today's parallel TPG's are mostly non-deterministic, i.e., the generated test set is timing and resource dependent, this complicates the debug process and may degrade the user experience. In this paper, we propose a multi-threading parallel test pattern generator that is both deterministic and incurs zero test inflation. Called SDC-TPG, the proposed parallel TPG relies on synchronized dynamic compaction (SDC) to generate the same test pattern set as the conventional serial TPG with dynamic compaction regardless of the thread timing and the thread count. Furthermore, an early primary fault TPG strategy is proposed to reduce the thread idle times and improve the speedup. Simulation results show that SDC-TPG achieves an average speedup of six with eight threads.

A GPU-based timing-aware ATPG is proposed to generate a compact high-quality test set. The test generation algorithm backtraces and propagates along multiple long paths so that many test patterns are generated at the same time. Generated test patterns are then fault simulated and selected. Compared with an 8-core CPU-based timing-aware commercial ATPG, the proposed GPU-based technique achieved 36% test length reductions on large benchmark circuits while the SDQL quality remains almost the same.

The applicability of at-speed scan-based logic built-in self-test (BIST) is being severely challenged by excessive capture power that may cause erroneous test responses for good chips. Different from conventional low-power BIST, this paper is the first that has explicitly focused on achieving capture power safety with a practical scheme called capture-power-safe BIST (CPS-BIST). The basic idea is to identify all possibly erroneous test responses and use the well-known technique of mask (partial-mask or full-mask) to block them from reaching the MISR. Experiments with large benchmark and industrial circuits show that CPS-BIST can achieve capture power safety with negligible impact on both test quality and area overhead.

Parallel programming is an attractive solution to accelerate test pattern generation (TPG); however, the associated non-determinism often leads to non-reproducible test pattern sets. In this paper, the circular pipeline processing (CPP) principle is proposed to facilitate deterministic parallel TPG. CPP preserves the task processing orders that are necessary to ensure TPG determinism with low inter-thread synchronization overhead. Based on CPP, a deterministic parallel test pattern generator is developed; it guarantees to produce the same test pattern set regardless of the thread timing and the thread count. Experimental results on benchmark circuits show that the proposed test pattern generator exhibits close-to-linear speedup for at least up to 12 threads.

This paper proposes a novel scheme to manage capture power in a pinpoint manner for achieving guaranteed capture power safety, improved small-delay test capability, and minimal test cost impact in at-speed scan test generation. First, switching activity around each long path sensitized by a test vector is checked to characterize it as hot (with excessively-high switching activity), warm (with normal/functional switching activity), or cold (with excessively-low switching activity). Then, X-restoration/X-filling-based rescue is conducted on the test vector to reduce switching activity around hot paths. If the rescue is insufficient to turn a hot path into a warm path, mask is then conducted on expected test response data to instruct the tester to ignore the potentially-false test response value from the hot path, thus achieving guaranteed capture power safety. Finally, X-restoration/X-filling-based warm-up is conducted on the test vector to increase switching activity around cold paths for improving their small-delay test capability. This novel approach of pinpoint capture power management has significant advantages over the conventionalapproachofglobalcapturepower management, as demonstrated by evaluation results on large ITC'99 benchmark circuits and detailed path delay analysis.

This article presents a hybrid Automatic Test Pattern Generation (ATPG) technique using the staggered Launch-On-Shift (LOS) scheme followed by the one-hot launch-on-shift scheme for testing delay faults in a scan design containing asynchronous clock domains. Typically, the staggered scheme produces small test sets but needs long ATPG runtime, whereas the one-hot scheme takes short ATPG runtime but yields large test sets. The proposed hybrid technique is intended to reduce test pattern count with acceptable ATPG runtime for multimillion-gate scan designs. In case the scan design contains multiple synchronous clock domains, and each group of synchronous clock domains is treated as a clock group and tested using a launch-aligned or a capture-aligned LOS scheme. By combining these schemes together, we found the pattern counts for two large industrial designs were reduced by approximately 1.6X to 1.8X, while the ATPG runtime was increased by 40% to 50%, when compared to the one-hot clocking scheme alone.

Test data compression is a much more difficult problem for launch-on-capture (LOC) delay testing, because test data for LOC delay testing is much more than that of stuck-at fault testing, and LOC delay fault test generation in the two-frame circuit model can specify many more inputs. A new scan architecture is proposed to compress test stimulus data, compact test responses, and reduce test application time for LOC delay fault testing. The new scan architecture merges a number of scan flip-flops into the same group, where all scan flip-flops in the same group are assigned the same values for all test pairs. Sufficient conditions are presented for including any pair of scan flip-flops into the same group for LOC transition, non-robust path delay, and robust path delay fault testing. Test data for LOC delay testing based on the new scan architecture can be compressed significantly. Test application time can also be reduced greatly. Sufficient conditions are presented to construct a test response compactor for LOC transition, non-robust, and robust path delay fault testing. Folded scan forest and test response compactor are constructed for further test data compression. Sufficient experimental results are presented to show the effectiveness of the method.

High power consumption in scan testing can cause undue yield loss which has increasingly become a serious problem for deep-submicron VLSI circuits. Growing evidence attributes this problem to shift timing failures, which are primarily caused by excessive switching activity in the proximities of clock paths that tends to introduce severe clock skew due to IR-drop-induced delay increase. This paper is the first of its kind to address this critical issue with a novel layout-aware scheme based on scan segmentation design, called LCTI-SS (Low-Clock-Tree-Impact Scan Segmentation). An optimal combination of scan segments is identified for simultaneous clocking so that the switching activity in the proximities of clock trees is reduced while maintaining the average power reduction effect on conventional scan segmentation. Experimental results on benchmark and industrial circuits have demonstrated the advantage of the LCTI-SS scheme.

This paper presents a hybrid automatic test pattern generation (ATPG) technique using the staggered launch-on capture (LOC) scheme followed by the one-hot LOC scheme for testing delay faults in a scan design containing asynchronous clock domains. Typically, the staggered scheme produces small test sets but needs long ATPG runtime, whereas the one-hot scheme takes short ATPG runtime but yields large test sets. The proposed hybrid technique is intended to reduce test pattern count with acceptable ATPG runtime for multi-million-gate scan designs. In case the scan design contains multiple synchronous clock domains, each group of synchronous clock domains is treated as a clock group and tested using a launch aligned or a capture aligned LOC scheme. By combining these schemes together, we found the pattern counts for two large industrial designs were reduced by approximately 1.1X to 2.1X, while the ATPG runtime was increased by 10% to 50%, when compared to the one-hot clocking scheme alone.

This paper presents a concurrent soft-error resilience (CSER) scheme with features that aid manufacturing test, online debug, and defect tolerance. The proposed CSER scheme is based on the built-in soft-error resilience (BISER) technique. A BISER cell is redesigned into various robust CSER cells that provide slow-speed snapshot, manufacturing test, slow-speed signature analysis, and defect tolerance capabilities. The cell-level area, power, and performance overhead of the robust CSER cells were found to be generally within 1% to 22% of the BISER cell.

This paper presents a new at-speed logic built-in self-test (BIST) architecture supporting two launch-on-capture schemes, namely aligned double-capture and staggered double-capture, for testing multi-frequency synchronous and asynchronous clock domains in a scan-based BIST design. The proposed architecture also includes BIST debug and diagnosis circuitry to help locate BIST failures. The aligned scheme detects and allows diagnosis of structural and delay faults among all synchronous clock domains, whereas the staggered scheme detects and allows diagnosis of structural and delay faults among all asynchronous clock domains. Both schemes solve the long-standing problem of using the conventional one-hot scheme, which requires testing each clock domain one at a time, or the simultaneous scheme, which requires adding isolation logic to normal functional paths across interacting clock domains. Physical implementation is easily achieved by the proposed solution due to the use of a slow-speed, global scan enable signal and reduced timing-critical design requirements. Application results for industrial designs demonstrate the effectiveness of the proposed architecture.

This paper presents fault modeling and analysis for resistive bridging defects in a synchronizer constructed with two D flip-flops. Bridging defects are exhaustively injected into any two nodes of the synchronizer to find all possible faults that might occur in the synchronizer, and HSPICE is used to perform circuit analysis.

This paper describes the logic built-in self-test (BIST) architecture for test and diagnosis of ASIC devices at the system level. The proposed architecture supports the at-speed staggered launch-on-capture clocking scheme and includes novel features to further increase the device's defect coverage, place-and-route ability, ease of debug and diagnosis, and reduce test power consumption. These features include equivalent clock merging for routing considerations, programmable shift modes for overheat considerations, configurable capture modes for yield loss and IR-drop considerations, as well as BIST signature diagnosis, masked-chain diagnosis, and one-chain diagnosis at the system level. Experimental results have successfully demonstrated the feasibility of using the proposed features for system-level test and diagnosis.

At-speed scan testing is susceptible to yield loss risk due to power supply noise caused by excessive launch switching activity. This paper proposes a novel two-stage scheme, namely CTX (Clock-Gating-Based Test Relaxation and X-Filling), for reducing switching activity when test stimulus is launched. Test relaxation and X-filling are conducted (1) to make as many FFs inactive as possible by disabling corresponding clock-control signals of clock-gating circuitry in Stage-1 (Clock-Disabling), and (2) to make as many remaining active FFs as possible to have equal input and output values in Stage-2 (FF-Silencing). CTX effectively reduces launch switching activity, thus yield loss risk, even with a small number of donpsilat care (X) bits as in test compression, without any impact on test data volume, fault coverage, performance, and circuit design.

TurboBIST-Logic (TBL) is a software tool suite for incorporating logic built-in self-test (BIST) technology into digital Integrated Circuits and has been used by a variety of industrial designs globally since 2002. This abstract describes major features of TBL, and uses three industrial cases to show practical issues encountered and solved over the years. It also discusses an important new trend in going "hybrid," a flexible combination of capture-clocking schemes, with the goal to achieve an ever more optimal result over stand-alone schemes. Each of the three cases had its unique requirements for logic BIST, some needing to customize an existing solution, but all were set to achieve common BIST goals of at-speed testing, simple test interface to/from ATE, low test cost, high product reliability, and repeat testability investment reuse from IC, board, system, to in-field diagnosis.

This paper describes a core-based test and diagnosis integration and automation system, called Turbo1500, which automatically synthesizes test and diagnosis logic in accordance with the IEEE 1500 standard. Turbo1500 serves two major purposes. One is for use as a core test automation tool in a system-on-chip (SOC) environment to automatically connect multiple cores from various sources and create testbenches each targeting an individual core under the control of a chip-level test access port (TAP) controller. The other is for hierarchical (block-by-block) core test and diagnosis when chips on a printed-circuit board are embedded with 1149.1 boundary scan I/O cells and cores under test and diagnosis are surrounded with 1500-compliant wrapper cells. Application experience showed that the simplicity of the IEEE 1500 standard combined with an easy-to-use automation tool can make core-based design for test and diagnosis no longer a nightmare, especially when some cores are extremely large or complex.

To test timing-related faults between synchronous clocks, an at-speed test clock and an automatic test pattern generation scheme are needed. However, previous work on designing on-chip at-speed test clock controllers for multi-clock has quadratic increasing area overhead along with linearly increasing clocks. This paper presents a clock-chain based test clock control scheme using an internal phase-locked-loop (PLL) as the at-speed test clock generator, which supports at-speed testing for inter-clock domain and intra-clock domain logic. Experimental results demonstrate that the proposed design has low area overhead when increasing the number of clocks.

The Test industry has come a long way over the past few decades. As a whole we have made great strides in the areas of:

High-quality at-speed scan testing, characterized by high small-delay-defect detecting capability, is indispensable to achieve high delay test quality for DSM circuits. However, such testing is susceptible to yield loss due to excessive power supply noise caused by high launch-induced switching activity. This paper addresses this serious problem with a novel and practical post-ATPG X-filling scheme, featuring (1) a test relaxation method, called path keeping X-identification, that finds don't-care bits from a fully-specified transition delay test set while preserving its delay test quality by keeping the longest paths originally sensitized for fault detection, and (2) an X-filling method, called justification-probability-based fill (JP-fill), that is both effective and scalable for reducing launch-induced switching activity. This scheme can be easily implemented into any ATPG flow to effectively reduce power supply noise, without any impact on delay test quality, test data volume, area overhead, and circuit timing.

We proposed clustered random access scan (CRAS) architecture to reduce test data volume. CRAS makes use of the compatibility of the test stimuli to cluster the scan cells, and assigns every cluster a unique address. The compression ratio upper bound of CRAS is analyzed based on the random graph theory. Experimental results on ISCAS'89 benchmarks and two industry designs show that the proposed CRAS architecture can yield on average 67.3% reduction in test data volume, with reasonable area and routing overhead than scan design

X-filling is preferred for low-capture-power scan test generation, since it reduces IR-drop-induced yield loss without the need of any circuit modification. However, the effectiveness of previous X-filling methods suffers from lack of guidance in selecting targets and values for X-filling. This paper addresses this problem with a highly-guided X-filling method based on two novel concepts: (1) X-score for X-filling target selection and (2) probabilistic weighted capture transition count for Y-filling value selection. Experimental results show the superiority of the new X-filling method for capture power reduction.

The quality of at-speed testing is being severely challenged by the problem that an inter-clock logic block existing between two synchronous clocks is not efficiently tested or totally ignored due to complex test control. This paper addresses the problem with a novel inter-clock at-speed test control scheme, featuring a compact and robust on-chip inter-clock enable generator design. The new scheme can generate inter-clock at-speed test clocks from PLLs, and is feasible for both ATE-based scan testing and logic BIST. Successful applications to industrial circuits have proven its effectiveness in improving the quality of at-speed testing

High power dissipation can occur when the response to a test vector is captured by flip-flops in scan testing, resulting in excessive JR drop, which may cause significant capture-induced yield loss in the DSM era. This paper addresses this serious problem with a novel test generation method, featuring a unique algorithm that deterministically generates test cubes not only for fault detection but also for capture power reduction. Compared with previous methods that passively conduct X-filling for unspecified bits in test cubes generated only for fault detection, the new method achieves more capture power reduction with less test set inflation. Experimental results show its effectiveness.

This paper describes a flexible logic BIST scheme that features high fault coverage achieved by fault-simulation guided test point insertion, real at-speed test capability for multi-clock designs without clock frequency manipulation, and easy physical implementation due to the use of a low-speed SE signal. Application results of this scheme to two widely used IP cores are also reported.

This paper presents an at-speed logic BIST architecture for testing multi-clock, multi-frequency designs. The scheme employed allows true at-speed test quality for circuits containing multiple clocks without any clock frequency manipulation. Physical implementation is easily achieved due to the use of a low-speed scan enable (SE) signal and reduced timing-critical design requirements. Application results for two industrial designs are also reported.

This paper describes time-division demultiplexing and multiplexing of high-data-rate scan patterns applied on I/O's into low-data-rate scan patterns applied on VirtualScan compression circuitry to further reduce test application time and test pin-count without coverage loss

Scan-based at-speed testing is a key technology to guarantee timing-related test quality in the deep submicron era. However, its applicability is being severely challenged since significant yield loss may occur from circuit malfunction due to excessive IR drop caused by high power dissipation when a test response is captured. This paper addresses this critical problem with a novel low-capture-power X-filling method of assigning 0's and 1's to unspecified (X) bits in a test cube obtained during ATPG. This method reduces the circuit switching activity in capture mode and can be easily incorporated into any test generation flow to achieve capture power reduction without any area, timing, or fault coverage impact. Test vectors generated with this practical method greatly improve the applicability of scan-based at-speed testing by reducing the risk of test yield loss.

This paper describes two design-for-test (DFT) methods that provide flexibility in order to achieve desired test cost reduction goal using embedded scan compression and logic built-in self-test (BIST). In some applications, one method can be used in conjunction with the other

Research on low-power scan testing has been focused on the shift mode, with little or no consideration given to the capture mode power. However, high switching activity when capturing a test response can cause excessive IR drop, resulting in significant yield loss. This paper addresses this problem with a novel low-capture-power X-filling method by assigning 0's and 1's to unspecified (X) bits in a test cube to reduce the switching activity in capture mode. This method can be easily incorporated into any test generation flow, where test cubes are obtained during ATPG or by X-bit identification. Experimental results show the effectiveness of this method in reducing capture power dissipation without any impact on area, timing, and fault coverage.

This work proposes a new per-test fault diagnosis method based on the X-fault model. The X-fault model represents all possible behaviors of a physical defect or defects in a gate and/or on its fanout branches by using different X symbols on the fanout branches. A novel technique is proposed for analyzing the relation between observed and simulated responses to extract diagnostic information and to score the results of diagnosis. Experimental results show the effectiveness of our method.

This work describes the VirtualScan technology for scan test cost reduction. Scan chains in a VirtualScan circuit are split into shorter ones and the gap between external scan ports and internal scan chains are bridged with a broadcaster and a compactor. Test patterns for a VirtualScan circuit are generated directly by one-pass VirtualScan ATPG, in which multi-capture clocking and maximum test compaction are supported. In addition, VirtualScan ATPG avoids unknown-value and aliasing effects algorithmically without adding any additional circuitry. The VirtualScan technology has achieved successful tape-outs of industrial chips and has been proven to be an efficient and easy-to-implement solution for scan test cost reduction.

A design technique is given for linear-feedback shift registers (LFSR) that generate test patterns for pseudoexhaustive testing of networks with restricted output dependency. This technique is based on cyclic code theory. Examples indicate that LFSRs based on cyclic codes are easier to implement and have lower hardware overhead than LFSRs that use other linear codes.>

Two hybrid schemes for the design of maximum-length sequence generators (MLSGs) are presented. Compared to an n-stage maximum-length LFSR (for generating 2/sup n/-1 nonzero distinct states) that uses m exclusive-or (XOR) gates, this hybrid MLSG will use exactly (m+1)/2 XOR gates if its characteristic polynomial meets certain requirements. For applications such as exhaustive testing, this hybrid MLSG is then reconfigured to include the all-zero state. It is shown that the reconfiguration is very simple and the hardware overhead is low.>

Implementation methods based on cyclic codes are presented for pseudoexhaustive testing of combinational logic networks with restricted output dependency. A modified linear-feedback shift register (LFSR) is used to generate exhaustive test patterns for every output of the circuit. All detectable, combinational faults (those that do not change a combinational circuit to a sequential circuit) in each cone of logic driving a single output are guaranteed to be detected. Examples indicate that LFSRs based on cyclic codes have lower hardware cost and shorter or comparable test lengths than other approaches. These test-pattern generators are well suited to applications where short testing time, low hardware overhead, and 100% single-stuck-at fault coverage are required.>

This paper presents a design technique for linear feedback shift registers that generate test patterns for pseudoexhaustive testing. This technique is applicable to any combinational network in which none of the outputs depends on all inputs. It does not rewire the original network inputs during in-circuit test pattern generation. Thus, the possibility of undetected faults on some inputs is eliminated.