Low-capture-power at-speed testing using partial launch-on-capture test scheme

Testing for delay faults in heavily gated clock designs has the major test challenges of reduced fault coverage and high test power consumption. In the scan-test method, gated clocks are often simplified and replaced with global test clocks. As such, partial clocking by the gated clocks is not inherited in test operations. Global clocking suffers from delay fault coverage loss because a sensitization state cannot easily be created due to the increased state dependence in functional paths, as compared to partial clocking. The global clocking scheme in the test mode is not adequate for low-power designs either, because the power consumed during a test operation exceeds that used during a normal operation. The power grid may not be sufficient to support the power drawn during testing, perhaps resulting in overkilled devices. It is therefore critical that power consumption be maintained under a safe limit, even during testing. In the proposed method, partial clocking in gated designs is preserved to the maximum possible to create more reachable states, thereby increasing transition fault coverage and reducing test power during launch and capture cycles. A transition fault simulator was developed, and it demonstrated higher transition fault coverage and reduced test power for ISCAS-89 circuits when partial clocking is used.

Excessive power dissipation caused by large amount of switching activities has been a major issue in scan-based testing. For large designs, the excessive switching activities during launch cycle can cause severe power droop, which cannot be recovered before capture cycle, rendering the at-speed scan testing more susceptible to the power droop. In this paper, we present a methodology to avoid power droop during scan capture without compromising at-speed test coverage. It is based on the use of a low area overhead hardware controller to control the clock gates. The methodology is ATPG (Automatic Test Pattern Generation)-independent, hence pattern generation time is not affected and pattern manipulation is not required. The effectiveness of this technique is demonstrated on several industrial designs.

Two-pattern tests for delay faults in standard scan circuits can be of one of two types: skewed-load or broadside. Each type of tests creates different conditions during test application due to the different way in which scan mode and functional mode are interleaved. Therefore, tests that are applicable both as skewed-load tests and as broadside tests are useful for comparing the two types of tests with respect to properties such as defect coverage or overtesting. In this work we investigate the possibility of generating tests that are applicable under both test application schemes. We refer to two-pattern tests that are applicable as both skewed-load and broadside tests as common-mode tests. We show that most benchmark circuits have sufficient numbers of common-mode tests to make them an interesting class of tests. Moreover, we show that the use of multiple scan chains increases the number of common-mode tests.

The conventional test-per-scan built-in self-test (BIST) scheme needs a number of shift cycles followed by one capture cycle. Fault effects received by the scan flip-flops are shifted out while shifting in the next test vector, like scan testing. Unlike deterministic testing, it is unnecessary to apply a complete test vector to the scan chains. A new scan-based BIST scheme is proposed by properly controlling the scan enable signals of the scan chains. Different weighted values are assigned to the scan enable signals of scan flip-flops in separate scan chains. Capture cycles can be inserted at any clock cycle if necessary. A new testability estimation procedure according to the proposed testing scheme is presented. A greedy procedure is proposed to select a weight for each scan chain. Experimental results show that the proposed method can improve test effectiveness of scan-based BIST greatly and most circuits can obtain complete fault coverage or very close to complete fault coverage.

Conventional shift-based scan chains have the drawback of peak power consumption which is reduced by the proposed single cycle access test structure for logic test. With the reduction of this power consumption the activity during shift and capture cycles have been achieved. In addition, more accurate circuit behavior can be achieved even at stuck-at and at-speed tests using the proposed methodology. Thereby it accomplishes close proximity to the functional mode during higher frequency operation tests. By using the proposed design minimum number of test cycles can be gained to the existed literature. It is observed that test cycles per net is below 1 for larger designs when tested for simple test pattern generator algorithm without test pattern compression. Has the advantage of autonomous of the plan estimate conjointly gives an extra on-chip investigating flag permeability for each enrols. It is in reverse congruous to the standard full check plans and with a minor improvement existing test design generators and test systems can be utilized conjointly talked about for the arrangement of including built-in self-test (BIST) and gigantic parallel check chains with the proposed plan. The design and implementation of single cycle access test structure for logic test is functionally verified using Vivado. The pre layout and post layout synthesis and its physical design are performed using cadence Genus and Innonus tools respectively, with the optimized area, power, and delay.

The random-like filling strategy pursuing high compression for scan test introduces large test power. To pursue high compression in conjunction with reducing test power for multiple scan chain designs is even harder and very few works were dedicated to solve this problem. This paper proposes and demonstrates a multilayer data copy (MDC) scheme for test compression as well as test power reduction for multiple scan designs. The scheme utilizes a buffer, which supports fast load using previous loaded data, to achieve test data compression and test power reduction at the same time. The scheme can be applied ATPG-independently or to be incorporated in an ATPG to generate highly compressible and power efficient test sets. Experiment results on benchmarks show that test sets generated by the scheme had large compression and power saving with little area design overhead

This paper studies the effect of the type of scan-based delay fault tests used for a circuit on the ability to diagnose delay defects by studying its effect on diagnosis of transition faults. The authors consider enhanced scan tests, skewed-load tests, broadside tests, functional broadside tests, and a combination of skewed-load and broadside tests. The results indicate that while functional broadside tests should be used for fault detection to avoid overtesting, the test set should be extended for fault diagnosis by adding other types of tests. Adding a small number of skewed-load tests is especially useful for diagnosis if enhanced scan is not available

Tester limitations may impose certain constraints on the primary input vectors applicable as part of a two-pattern test for delay faults. Under these constraints, the primary input vectors may be held constant, or the second primary input vector of a test may be obtained by a single shift of a scan chain relative to the first. The goal of this brief is to study the differences in achievable transition fault coverage between various primary input constraints that are similar to the commonly used ones of holding or shifting primary input vectors. This brief also studies the possibility of combining the constraints in order to increase the transition fault coverage. The combination requires a fixed and circuit-independent hardware structure similar to the case where shifting of primary input vectors is used. This study is done using test sets that consist of both broadside and skewed-load tests in order to maximize the transition fault coverage.

This paper presents three built-in self-test (BIST) schemes for robust testing of stuck-open faults in combinational FCMOS complex cells of arbitrary structure. The first method shows that all single stuck-open faults can be robustly tested by applying a universal sequence of 5/spl times/2/sup n/ vectors to the modified circuit under test (CUT), and counting the number of 1's in the output response. The second method uses the same test pattern generator (TPG), but faults are detected by a self comparison technique without the need of storing a signature. Finally, we propose a new adaptive BIST technique, where the TPG is driven by the past outputs of the CUT itself In all the cases, the TPG is universal, i.e., if does not depend on the functionality and the structure of the CUT, but does ensure robust testing. Neither any test vector, nor any fault dictionary, is required. These approaches provide simplicity, less testing time and test data, and compare favorably with earlier BIST designs for CMOS circuits.

At-speed scan testing has become mandatory due to the extreme CMOS technology scaling. The two main at-speed scan testing schemes are namely Launch-Off-Shift (LOS) and Launch-Off-Capture (LOC). As it can be easily implemented, LOC has been widely investigated in the literature in the last few years, especially regarding test power consumption. Conversely, LOS has received much less attention. In this paper, we propose a comparison between the two testing schemes in terms of transition fault coverage and power consumption, in order to quantify the pros and cons of LOS with respect to LOC. This study shows that LOS not only exhibits higher performance in coverage but also does not require as much extra power as predicted, especially in terms of peak power. These facts may represent convincing arguments for its wider use and development.

The speed of new VLSI designs is rapidly increasing. Assuring the performance of the circuit requires that the circuit be tested at its intended operating speed. The high cost of high speed testers makes it impossible for the testers to follow the designs in terms of speed increase. This gap between the speed of the new circuits and the speed of the testers is not likely to disappear. In this paper, we focus on at-speed strategies for testing high speed designs on slower testers. Conventional at-speed testing strategies assume that the primary inputs/outputs can be applied/observed at the circuit rated speed. This requires a high speed tester. Our assumption is that a fast clock matching the speed of the designs is available. We describe two classes of at-speed strategies that can be used on a low speed tester. The first class consists of testing schemes for which the test generation procedure is independent of the speed of the tester. These methods apply multiple input patterns in one tester cycle and the test application time for them can be long. The strategies in the second class of at-speed testing schemes integrate the tester's speed limitations with the test generation process. Due to constraints placed at the test generation process, these schemes might result in a reduced fault coverage. To increase the fault coverage and reduce the test application time, the slow-fast-slow and at-speed strategies can be combined for testing high speed designs on slower testers. We present preliminary experimental results for at-speed schemes for slow testers for transition faults.

Test generation procedures target a variety of fault models in order to produce test sets that are effective for defect detection. This paper considers the likely scenario where two-cycle skewed-load tests are generated to detect single transition faults, and the test set is complemented with tests for single stuck-at faults that are not detected by the transition fault test set. For this scenario, this paper makes several unique observations that can be utilized to produce a single compact test set that consists only of two-cycle skewed-load tests for both fault models. The first observation is that a single-cycle test for a stuck-at fault can be transformed into a skewed-load test that is guaranteed to detect the stuck-at fault without performing logic or fault simulation. The second observation is that skewed-load tests, which are transformed from single-cycle tests for stuck-at faults, sometimes detect more transition and stuck-at faults than tests that were generated for transition faults. The third observation is that a static test compaction procedure, which is based on the modification and removal of tests, is effective in this context because it allows tests for stuck-at faults to detect more transition faults and vice versa. This paper describes a test compaction procedure based on these observations and presents experimental results for benchmark circuits to demonstrate the effectiveness of the procedure.

The excessive power consumption during testing has been a critical issue for scan-based designs. It gets even worst in the capture mode. This method combines testability-aware test pattern generation with the scan chain disabling technique for low capture power scan testing. The observability cost in the SCOAP algorithm is purposely skewed to guide most fault effects to a limited number of scan cells. Combined with the subsequent scan chain clustering and scan chain disabling techniques, as many non-used scan chains can be disabled during capture cycles. The required hardware overhead for clock gating is limited. Experimental results for the larger ISCAS'89 benchmark circuits have demonstrated that 75.96% of capture power reduction can be achieved.

Test compression has become a de facto technique in VLSI testing. Meanwhile, excessive capture power of at-speed testing has also become a serious concern. Therefore, it is important to co-optimize test power and compression ratio in at-speed testing. In this paper, a novel X-filling framework is proposed to reduce capture power of both LoC and LoS at-speed testing, which is applicable for different test compression schemes. The proposed technology has been validated by the experimental results on larger ITC'99 benchmark circuits.

A double edge clipping technique is proposed for at-speed BIST testing. It differs from traditional circuit delay testing techniques by changing the clock rate using external ATE. This method uses lower-speed input clock frequency, then applies internal BIST circuit to adjust clock edges for circuit at-speed delay testing and speed binning. This built-in at-speed delay test with calibration mechanism named as double edge clipping (DEC) technique. DEC is based on the lunch on shift (LOC) scheme by precisely controlling the launch and capture edges during delay test operation. Two wide-range (26% -80%), fine-scale (16ps) duty cycle adjustment circuits with high-precision (28ps) calibration mechanism are effective applied for at-speed delay testing and performance binning. The key to DEC testing technique is to generate a pair of clock pulses for the launch and capture events. Two DCPG provide adjusted positive clock edge during test operation. DEC uses 500kHz low speed input clock then provides working clock frequency from 197MHz to 932MHz.