In this paper, a cost efficient test methodology to screen chips that have resistive open defects under the presence of process variation is proposed. The proposed test methodology is based on small delay defect testing. The entire test session is divided into several subsessions. In each subsession, test patterns are applied with a different frequency of test clock, all of which are faster than the rated clock. Unlike others, different test patterns are generated and applied in each subsession to reduce test application time. A simple three step screening method is also proposed. The first step identifies scan outputs that can fail only if there are defects under the possible worst case process variation. In the second step, we assume that a chip failed due to a defect if the number of faulty scan outputs in a test pattern is much larger than that of faulty scan outputs of a typical defect free chip. Finally, the third step screens defective chips by comparing the number of fail patterns. Among 10 benchmark circuits used for the experiments, the proposed method was able to screen successfully more than 90% of defective chips for 8 circuits.

A self-diagnosis circuit that can be used for built-in self-repair is proposed. The circuit under diagnosis is assumed to be composed of a large number of field repairable units (FRUs), which can be replaced with spares when they are found to be defective. Since the proposed self-diagnosis circuit is implemented on the chip, responses that are scanned out of scan chains are compressed by the group compactor, the space compression circuit, and finally, the time compression circuit to reduce the volume of test response data. Both the space and time compression circuits implement a Reed-Solomon code. Unlike prior work, in the proposed technique, responses of all FRUs are observed at the same time to reduce diagnosis time. The proposed diagnosis circuit can locate up to l defective FRUs. We propose a novel space compression circuit that reduces hardware overhead by exploiting the frequency difference of the scan shift clock and the system clock and by combining scan cells into groups of size r. When the size of constituent multiple-input signature register (MISR) is m, the total number of signatures to be stored for the fault-free signature is 2 lmB bits, where 1≤ B ≤ m. The experimental results show that the proposed diagnosis circuit that can locate up to four defective FRUs in the same test session can be implemented with less than one percent of hardware overhead for a large industrial design. Hardware overhead for the diagnosis circuit is lower for large CUDs.

This paper presents a test data compression scheme that can be used to further improve compressions achieved by linear-feedback shift register (LFSR) reseeding. The proposed compression technique can be implemented with very low hardware overhead. The test data to be stored in the automatic test equipment (ATE) memory are much smaller than that for previously published schemes, and the number of test patterns that need to be generated is smaller than other weighted random pattern testing schemes. The proposed technique can be extended to generate test patterns that achieve high n-detection fault coverage. This technique compresses a regular 1-detection test cube set instead of an n-detection test cube set, which is typically n times larger. Hence, the volume of compressed test data for n-detection test is comparable to that for 1-detection test. Experimental results on a large industry design show that over 1600X compression is achievable by the proposed scheme with the test sequence length, which is comparable to that of highly compacted deterministic patterns. Experimental results on n -detection test show that test patterns generated by the proposed decompressor can achieve very high 5-detection stuck-at fault coverage and high compression for large benchmark circuits.

In this paper, a novel diagnosis method is proposed. The proposed technique uses machine learning techniques instead of traditional cause-effect and/or effect-cause analysis. The proposed technique has several advantages over traditional diagnosis methods, especially for volume diagnosis. In the proposed method, since the time consuming diagnosis process is reduced to merely evaluating several decision functions, run time complexity is much lower than traditional diagnosis methods. The proposed technique can provide not only high resolution diagnosis but also statistical data by classifying defective chips according to locations of their defects. Even with highly compressed output responses, the proposed diagnosis technique can correctly locate defect locations for most defective chips. The proposed technique correctly located defects for more than 90% (86%) defective chips at 50times (100times) output compaction. Run time for diagnosing a single simulated defect chip was only tens of milli-seconds.

A self-diagnosis circuit that can be used for builtin self-repair is proposed. The circuit under diagnosis is assumed to be comprised of a large number of field repairable units (FRUs), which can be replaced with spares when they are found to be defective. Since the proposed self-diagnosis circuit is implemented on the chip, responses that are scanned out of scan chains are compressed first by the space compression circuit and then by the time compression circuit to reduce the volume of test response data. Both the space and the time compression circuit implement a Reed-Solomon code. Unlike prior work, in the proposed technique, responses of all FRUs are observed at the same time to reduce diagnosis time. The proposed diagnosis circuit can locate up to l defective FRUs. We propose a novel space-compression circuit that reduces hardware overhead by exploiting the frequency difference of the scan shift clock and the system clock. When the size of constituent multiple-input signature-register (MISR) is m, the total number of signatures to be stored for the fault-free signature is 2lmB bits, where 1 les B les m. The experimental results show that the proposed diagnosis circuit that can locate up to 4 defective FRUs in the same test session can be implemented with less than 1% of hardware overhead for a large industrial design. Hardware overhead for the diagnosis circuit is lower for large CUDs.

We present a system-on-chip (SOC) testing approach that integrates test data compression, test-access mechanism/test wrapper design, and test scheduling. An efficient linear feedback shift register (LFSR) reseeding technique is used as the compression engine. All cores on the SOC share a single on-chip LFSR. At any clock cycle, one or more cores can simultaneously receive data from the LFSR. Seeds for the LFSR are computed from the care bits for the test cubes for multiple cores. We also propose a scan-slice-based scheduling algorithm that attempts to maximize the number of care bits the LFSR can produce at each clock cycle, such that the overall test application time (TAT) is minimized. This scheduling method is static in nature because it requires predetermined test cubes. We also present a dynamic scheduling method that performs test compression during test generation. Experimental results for International Symposium on Circuits and Systems and International Workshop on Logic and Synthesis benchmark circuits, as well as industrial circuits, show that optimum TAT, which is determined by the largest core, can often be achieved by the static method. If structural information is available for the cores, the dynamic method is more flexible, particularly since the performance of the static compression method depends on the nature of the predetermined test cubes.

This paper presents techniques to improve compressions by improving fault coverage that can be achieved by broadcast scan. Due to reconvergent gates that artificially occur in broadcast scan, broadcast scan fault coverage is often much lower than standard serial scan fault coverage. The proposed scan chain reordering technique improves broadcast scan fault coverage by minimizing the number of reconvergent gates and hence no or very small number of test patterns are required to be applied by standard serial scan to detect faults undetected by broadcast scan. This increases the overall compression ratio. To eliminate or minimize increase in routing overhead, the distance that each scan cell can be relocated by the scan chain reordering procedure is limited. Test points are inserted to further reduce correlation among outputs of scancells. The proposed scan chain reordering technique improved broadcast scan fault converge by up to 8.5%. Large fault coverage improvement was achieved by the proposed method, especially for circuits that suffer low broadcast scan fault coverage. Broadcast scan fault coverage for the largest two industrial designs was even higher than standard serial scan fault coverage.

This paper presents a scan-based DFT technique that uses limited number of enhanced scan cells to reduce volume of delay test patterns and improve delay fault coverage. The proposed method controls a small number of enhanced scan cells by the skewed-load approach and the rest of scan cells by the broadside approach. Inserting enhanced scan cells reduces test data volume and ATPG run time and improves delay fault coverage. Hardware overhead for the proposed method is very low. The scan inputs where enhanced scan cells are inserted are selected by gain functions, which consist of controllability costs and usefulness measures. A regular ATPG can be used to generate transition delay test patterns for the proposed method. Experimental results show that test data volume is reduced by up to 65% and fault coverage is improved by up to about 6%.

This paper presents an efficient method to block unknown values for temporal compactors. The control signals for the blocking logic are generated by a linear feedback shift register (LFSR). Control patterns, which describe values required at the control signals of the blocking logic, are compressed by LFSR reseeding. The size of the control LFSR, which is determined by the number of specified bits in the most specified control pattern, is minimized by propagating only one fault effect for each fault and targeting the faults that are uniquely detected by each test pattern. The linear solver to find seeds of the LFSR intelligently chooses a solution such that the impact on test quality is minimal. Very high compression (over 230X) is achieved for benchmark and industrial circuits by the proposed method. Experimental results show that the sizes of control data for the proposed method are smaller than prior work and the runtime of the proposed method is several orders of magnitude smaller than that of prior work. Hardware overhead is very low.

This paper presents an efficient method to block unknowns for temporal compactors. The proposed blocking logic can reduce data volume required to control the blocking logic and increase the number of scan cells that are observed by temporal compactors. Control patterns, which specify values required at the control signals of the blocking logic, are compressed by linear feedback shift register reseeding. In this paper, the blocking logic gates for some scan chains that do not capture unknowns are bypassed. Since all scan cells in these scan chains can be observed without specifying the corresponding bits in control patterns, more scan cells are observed while a smaller number of bits are required to be specified. The seed size is further reduced by reducing the numbers of specified bits in the densely specified control patterns. The proposed method can always achieve the same fault coverage that can be achieved by directly observing scan chains without any output compaction. Experiments with large industrial designs clearly demonstrate that the proposed method is scalable to large circuits. Hardware overhead for the proposed unknown blocking scheme is very low.

In this paper, a technique that can efficiently reduce peak and average switching activity during test application is proposed. The proposed method does not require any specific clock tree construction, special scan cells, or scan chain reordering. Test cubes generated by any combinational ATPG can be processed by the proposed method to reduce peak and average switching activity without any capture violation. Switching activity during scan shift cycles is reduced by assigning identical values to adjacent scan inputs and switching activity during capture cycles is reduced by limiting the number of scan chains that capture responses. Hardware overhead for the proposed method is negligible. The peak transition is reduced by about 40% and average number of transitions is reduced by about 56-85%. This reduction in peak and average switching activity is achieved with no decrease in fault coverage.

This paper presents a test data compression scheme that can be used to further improve compressions achieved by LFSR reseeding. The proposed compression technique can be implemented with very low hardware overhead. Unlike most commercial test data compression tools, the proposed method requires no special ATPG that is customized for the proposed scheme and can be used to compress test patterns generated by any ATPG tool. The test data to be stored in the ATE memory are much smaller than that for previously published schemes and the number of test patterns that need to be generated is smaller than other weighted random pattern testing schemes. Experimental results on a large industry design show that over 1600X compression is achievable by the proposed scheme with the number of patterns comparable to that of highly compacted deterministic patterns.

We present an SoC testing approach that integrates test data compression, TAM/test wrapper design, and test scheduling. An improved LFSR reseeding technique is used as the compression engine. All cores on the SoC share a single on-chip LFSR. At any clock cycle, one or more cores can simultaneously receive data from the LFSR. Seeds for the LFSR are computed from the core bits from the test cubes for multiple cores. We also propose a scan-slice-based scheduling algorithm that tries to maximize the number of core bits the LFSR can produce at each clock cycle, such that the overall test application time is minimized. Experimental results for both ISCAS circuits and industrial circuits show that optimal test application time, which is determined by the largest core, can be achieved. The proposed approach has small hardware overhead and is easy to deploy. Only one LFSR, one phase shifter, and a few counters should be added to the SoC. The scheduling algorithm is also scalable for large industrial circuits. The CPU time for a large industrial design ranges from 1 to 30 minutes

This paper presents a new blocking logic to block unknowns for temporal compactors. The proposed blocking logic can reduce data volume required to control the blocking logic and also increase the number of scan cells that are observed by the temporal compactors. Control patterns, which describe values required at the control signals of the blocking logic, are compressed by LFSR reseeding. In this paper, the blocking logic gates for some groups of scan chains that do not capture unknowns are bypassed. Since all the scan cells in these scan chain groups are observed without specifying the corresponding bits in control patterns, fewer specified bits are required and more scan cells are observed. The seed size is further reduced by reducing numbers of specified bits in the densely specified control patterns. The proposed method can always achieve the same fault coverage that can be achieved by direct observation of scan chains. Experiments with large industrial designs clearly demonstrate that the proposed method is scalable to large circuits. Hardware overhead for the proposed blocking logic is very low

This paper presents a hybrid compaction scheme for test responses containing unknown values, which consists of a space compactor and an unknown-blocking Multiple Input Signature Registers (MISR). The proposed scheme guarantees no coverage loss for the modeled faults. The proposed hybrid scheme can also be tuned to observe any user- specified percentage of responses for controlling the coverage loss for un-modeled faults. The experimental results demonstrate that, in comparison with a space compactor or an unknown-blocking MISR alone, the hybrid compaction scheme achieves a lower coverage loss without demanding more test-data volume. In addition, we propose a quantitative approach to estimate the required percentage of observable responses for the proposed scheme, directly based on a test-quality metric of un-modeled faults.

This paper presents a test data compression scheme that combines weighted random pattern testing and LFSR reseeding. Test patterns generated by the proposed decompressor can achieve high n-detection fault coverage. The proposed technique computes weight sets from a set of test cubes that are generated by a traditional 1-detection ATPG tool. The computed weight sets are modified to achieve high ndetection fault coverage. The proposed decompressor can be implemented with low area overhead. Since the proposed technique requires no special ATPG that is customized for the proposed scheme, it can compress test patterns generated by any ATPG tool and generate test patterns from the compressed test data that achieve high n-detection fault coverage. Experimental results show that test patterns generated by the proposed decompressor can achieve very high 5- detection stuck-at fault coverage and high compression for large benchmark circuits

This paper presents a low hardware overhead test pattern generator (TPG) for scan-based built-in self-test (BIST) that can reduce switching activity in circuits under test (CUTs) during BIST and also achieve very high fault coverage with reasonable lengths of test sequences. The proposed BIST TPG decreases transitions that occur at scan inputs during scan shift operations and hence reduces switching activity in the CUT. The proposed BIST is comprised of two TPGs: LT-RTPG and 3-weight WRBIST. Test patterns generated by the LT-RTPG detect easy-to-detect faults and test patterns generated by the 3-weight WRBIST detect faults that remain undetected after LT-RTPG patterns are applied. The proposed BIST TPG does not require modification of mission logics, which can lead to performance degradation. Experimental results for ISCAS'89 benchmark circuits demonstrate that the proposed BIST can significantly reduce switching activity during BIST while achieving 100% fault coverage for all ISCAS'89 benchmark circuits. Larger reduction in switching activity is achieved in large circuits. Experimental results also show that the proposed BIST can be implemented with low area overhead.

Since structured application specific integrated chip (ASIC) products require very short turn around time, long automatic test pattern generation (ATPG) run time is undesirable. Large structured ASICs often require a large number of test patterns to achieve the desired fault coverage. This paper presents the first test point insertion technique for structured ASICs that can reduce test set sizes and ATPG run time. Only unused flip-flops in the structured ASIC design are used to implement test points, so the proposed technique does not incur any hardware overhead. Since test points are inserted during a post-layout step, considering both timing and layout information, hence test points can be inserted without changing the existing layout or routing. Novel gain functions are defined that specifically quantify the reduction in test volume and test time to select the best signal lines for inserting test points. The gain function described in this paper is also applicable to regular cell based ASICs. The proposed test point insertion technique can be used in conjunction with any compression technique (Jas et al., 2003) to further reduce the test volume. Experimental results clearly demonstrate the effectiveness and scalability of the proposed technique. Using less than 1% of extra flip-flops and very little run time for test point insertion, test generation time was reduced by up 42.9% and test data volume by up to 25.9% while also achieving a near 100% fault efficiency for very large industrial (400K-5M signal lines) designs

For a space compactor, degradation of fault detection capability caused by the masking effects from unknown values is much more serious than that caused by error masking (i.e. aliasing). In this paper, we first propose a mathematical framework to estimate the percentage of observable responses under unknown-induced masking for a space compactor. We further develop a prediction scheme which can correlate the percentage of observable responses with the modeled-fault coverage and with a n-detection metric for a given test set. As a result, the quality of a space compactor can be measured directly based on its test quality, instead of based on indirect metrics such as the number of tolerated unknowns or the aliasing probability. With the prediction scheme above, we propose a construction flow for space compactors to achieve the desired level of test quality while maximizing the compaction ratio.

The presence of unknown values in simulation is the great est barrier to effective test response compaction. For space compactors, some responses may not be observable due to the masking effect caused by unknown values. This paper reports on experiments conducted to evaluate the impact on the test quality of various percentages of observable responses for both modeled and un-modeledfaults.

This paper presents an efficient method to block unknown values from entering temporal compactors. The control signals for the blocking logic are generated by an LFSR. The proposed technique minimizes the size of the LFSR by propagating only one fault effect for each fault and balancing the number of specified bits in each control pattern. The linear solver to find seeds of the LFSR intelligently chooses a solution such that the impact on test quality is minimal. Experimental results show that sizes of control data for the proposed method are smaller than prior work and run time of the proposed method is several orders of magnitude smaller than that of prior work. Hardware overhead is very low.

In this paper, an automatic test pattern generator (ATPG)-based scan-path test point insertion technique, which can achieve high delay fault coverage for scan designs, is proposed. In the proposed technique, the shift dependency between adjacent scan flip-flops, which causes some delay faults to be untestable in the standard scan environment, is broken by inserting test points, which can be combinational gates as well as flip-flops. Instead of topology-based approaches used in prior publications, the proposed technique uses a special ATPG to identify pairs of adjacent scan flip-flops between which test points are inserted to improve fault coverage. Since the proposed technique inserts test points only where they are necessary, it can drastically reduce hardware overhead compared to circuit topology-based techniques. One hundred percent transition delay coverage was attained for all ISCAS 89 benchmark circuits except one. This is achieved with very small numbers of test points. On average, about 40% reduction in scan chain length against a prior approach was achieved by the proposed method for benchmark circuits with default scan chain order.

A new built-in self-test (BIST) test pattern generator (TPG) design, called low-transition random TPG (LT-RTPG), is presented. An LT-RTPG is composed of a linear feedback shift register (LFSR), a /spl kappa/-input AND gate, and a T flip-flop. When used to generate test patterns for test-per-scan BIST, it decreases the number of transitions that occur during scan shifting and, hence, decreases switching activity during testing. Various properties of LT-RTPGs are identified and a methodology for their design is presented. Experimental results demonstrate that LT-RTPGs designed using the proposed methodology decrease switching activity during BIST by significant amounts while providing high fault coverage.

The presence of unknown values in the simulation result is a key barrier to effective output response compaction in practice. This paper proposes a simple circuit module, called a response shaper, to reshape the scan-out responses before feeding them to a space compactor. Along with the proposed reshaping algorithm, response shapers can help the space compactor to reduce the number of undetectable modeled and unmodeled faults in the presence of unknown values. Moreover, the proposed compaction scheme is ATPG-independent and its hardware requirement is pattern-independent. In our experiments, we use a simple XOR compactor as the space compactor to evaluate the effectiveness of the response shaper. The results show that the number of undetectable faults and unobservable scan-out responses can be significantly reduced in comparison with the results of a convolutional compactor. The number of the extra scan-in bits required for the control signals of the response shapers is only a small fraction of the total test data volume. Also, its hardware overhead is acceptable and the runtime of the reshaping algorithm is scalable for large industrial designs.

This paper proposes a response compactor, named ChiYun compactor, to compact scan-out responses in the presence of unknown values. By adding storage elements into an Xor network, a ChiYun compactor can offer multiple chances for a scan-out response to be observed at ATE channels in one to several scan-shift cycles. We also develop a mathematical analysis to predict the percentage of scan-out responses masked by the unknown values for the ChiYun compactor. With this analysis, we can derive the optimal configuration of a ChiYun compactor for minimizing the masking of scan-out responses. We further propose a selection scheme for the ChiYun compactor to selectively observe partial Xor results for improving the fault coverage. The experimental results demonstrate the effectiveness of the proposed mathematical analysis and the selection scheme. We also demonstrate that the unknown tolerance of a ChiYun compactor is higher than that of a state-of-the-art response compactor proposed in (Wang, 2003).

This paper presents an input test data compression scheme that combines the advantages of weighted pseudorandom testing techniques and LFSR reseeding. The scheme requires low area overhead and the compression achieved is not limited by the LFSR reseeding bounds. The test data storage requirements of both the static and dynamic versions of the proposed scheme are lower than previously published results. The total numbers of test patterns that need to be applied are much lower than that for any weighted pseudorandom testing or hybrid BIST scheme. Further, the method provides an easy way to trade off between test application time and test data compression. The static version of the scheme can be easily implemented without any modification to the current test generation flow while the dynamic version can be used if the ATPG can be modified. Experimental results on a large industry design show that over 100/spl times/ compression is achievable by the proposed scheme.

A novel scan-based delay test approach, referred as the hybrid delay scan, is proposed in this paper. The proposed scan-based delay testing method combines advantages of the skewed-load and broad-side approaches. Unlike the skewed-load approach whose design requirement is often too costly to meet due to the fast switching scan enable signal, the hybrid delay scan does not require a strong buffer or buffer tree to drive the fast switching scan enable signal. Hardware overhead added to standard scan designs to implement the hybrid approach is negligible. Since the fast scan enable signal is internally generated, no external pin is required. Transition delay fault coverage achieved by the hybrid approach is equal to or higher than that achieved by the broad-side load for all ISCAS 89 benchmark circuits. On an average, about 4.5% improvement in fault coverage is obtained by the hybrid approach over the broad-side approach.

In this paper,an automatic test pattern generator (ATPG)-based scan-path test point insertion technique,which can achieve high delay fault coverage for scan designs,is proposed. In the proposed technique,the shift dependency between adjacent scan flip-flops,which causes some delay faults to be untestable in the standard scan environment,is broken by inserting test points,which can be combinational gates as well as flip-flops. Instead of topology-based approaches used in prior publications,the proposed technique uses a special ATPG to identify pairs of adjacent scan flip-flops between which test points are inserted to improve fault coverage. Since the proposed technique inserts test points only where they are necessary,it can drastically reduce hardware overhead compared to circuit topology-based techniques. One hundred percent transition delay coverage was attained for all ISCAS 89 benchmark circuits except one. This is achieved with very small numbers of test points. On average,about 40% reduction in scan chain length against a prior approach was achieved by the proposed method for benchmark circuits with default scan chain order. Index Terms—Delay fault,scan testing,test point insertion,transition delay fault.

This paper presents a low hardware overhead test pattern generator (TPG) for scan-based BIST that can reduce switching activity in CUTs during BIST and also achieve very high fault coverage with a reasonable length of test sequence. Since the correlation between consecutive vectors applied to a circuit during BIST is significantly lower, switching activity in the circuit can be significantly higher during BIST than that during its normal operation. Excessive switching activity during test application can damage CUTs during BIST. The proposed BIST decreases the number of transitions that occur at scan inputs during scan shift operations and hence decreases switching activity during BIST. The proposed BIST is comprised of two TPGs: LT-RTPG and 3-weight WRBIST TPG, both of which are proposed in previous publications. This paper shows that the 3-weight WRBIST TPG, which is used to detect random pattern resistant faults, can also be used to reduce switching activity in CUTs during BIST. Experimental results also show that the proposed BIST can be implemented with very low area overhead.

A test pattern generator (TPG) for built-in self-test (BIST), which can reduce switching activity during test application, is proposed. The proposed TPG, called dual-speed LFSR (DS-LFSR), consists of two linear feedback shift registers (LFSRs), a slow LFSR and a normal-speed LFSR. The slow LFSR is driven by a slow clock whose speed is 1/dth that of the normal clock, which drives the normal-speed LFSR. The use of DS-LFSR reduces the frequency of transitions at the circuit inputs driven by the slow LFSR, leading to a reduction in switching activity during test application. A procedure is presented to design a DS-LFSR so as to achieve high fault coverage by ensuring that patterns generated by it are unique and uniformly distributed. A new gain function and a method to compute its value for each circuit input are proposed to select inputs to be driven by the slow LFSR. Also, a procedure to increase the number of inputs driven by the slow LFSR by combining compatible inputs is presented to further decrease the switching activity. Finally, DS-LFSRs are designed for the ISCAS85 and ISCAS89 benchmark circuits and shown to provide a 13% to 70% reduction in the numbers of load-capacitance weighted transitions with no loss of fault coverage (for stuck-at as well as transition delay faults) and at very slight area overheads.

An automatic test pattern generation (ATPG) technique is proposed that reduces switching activity during testing of sequential circuits that have full scan. The objective is to permit safe and inexpensive testing of low-power circuits and bare dies that would otherwise require expensive heat removal equipment for testing at high speed. The approach works with standard scan designs that are commonly used and typically have significantly lower overhead than enhanced scan designs. The proposed ATPG exploits all possible "don't cares" that occur during scan shifting, test application, and response capture to minimize switching activity in the circuit under test. An ATPG that minimizes the number of state inputs that are assigned specific binary values has been developed. Don't cares at state inputs are assigned binary values that cause the minimum number of transitions during scan shifting and don't cares at primary inputs during scan shifting and capture are used to block gates that may have transitions during scan shifting. The proposed technique has been implemented and the generated tests are compared with those generated by a simple PODEM implementation for full scan versions of ISCAS89 benchmark circuits.

A new BIST TPG design, called low-transition random TPG (LT-RTPG), that is comprised of an LFSR, a k-input AND gate, and a T flip-flop, is presented. When used to generate test patterns for test-per-scan BIST, it decreases the number of transitions that occur during scan shifting and hence decreases the heat dissipated during testing. Various properties of LT-RTPGs are studied and a methodology for their design is presented. Experimental results demonstrate that LT-RTPGs designed using the proposed methodology decrease the heat dissipated during BIST by significant amounts while attaining high fault coverage, especially for circuits with moderate to large number of scan inputs.

A automatic test pattern generator (ATPG) algorithm is proposed that reduces switching activity (between successive test vectors) during test application. The main objective is to permit safe and inexpensive testing of low power circuits and bare die that might otherwise require expensive heat removal equipment for testing at high speeds, Three new cost functions, namely transition controllability, observability, and test generation costs, have been defined. It has been shown, for a fanout free circuit under test, that the transition test generation cost for a fault is the minimum number of transitions required to test a given stuck-at fault. The proposed algorithm has been implemented and the generated tests are compared with those generated by a standard PODEM implementation for the larger ISCAS85 benchmark circuits. The results clearly demonstrate that the tests generated using the proposed ATPG can decrease the average number of (weighted) transitions between successive test vectors by a factor of 2 to 23.

An ATPG technique is proposed that reduces heat dissipationduring testing of sequential circuits that have full-scan. The objectiveis to permit safe and inexpensive testing of low power circuitsand bare die that would otherwise require expensive heat removalequipment for testing at high speeds. The proposed ATPG exploitsall don't cares that occur during scan shifting, test application, andresponse capture to minimize switching activity in the circuit undertest. Furthermore, an ATPG that maximizes the number of state inputsthat are assigned don't care values, has been developed. Theproposedtechniquehas beenimplemented and usedto generatetestsfor full scan versions of ISCAS 89 benchmark circuits. These testsdecrease the average number of transitions during test by 19% to89%, when comparedwith those generatedby a simple PODEM implementation.

A test pattern generator (TPG) for built-in self-test (BIST), which can reduce heat dissipation during test application, is proposed. The proposed TPG, called dual-speed LFSR (DS-LFSR), consists of two linear feedback shift registers (LFSRs), a slow LFSR and a normal-speed LFSR. The slow LFSR is driven by a slow clock whose speed is width that of the normal clock which drives the normal-speed LFSR, The use of DS-LFSR lowers the transition density at the circuit inputs driven by the slow LFSR, leading to a reduction in heat dissipation during test application. A procedure is presented to design a DS-LFSR so as to achieve high fault coverage by ensuring that patterns generated by it are unique and uniformly distributed. A new gain function, and a method to compute its value for each circuit input, is proposed to select inputs to be driven by the slow LFSR. Also, a procedure to increase the number of inputs driven by the slow LFSR by combining compatible inputs is presented to further decrease the heat dissipation, Finally, DS-LFSRs are designed for the ISCAS85 and ISCAS89 benchmark circuits and shown to provide 13% to 70% reduction in the numbers of transitions with no loss of fault coverage and at very slight area overheads.

A new ATPG algorithm has been proposed that reduces average heat dissipation (between successive test vectors) during test application. The objective is to permit safe and inexpensive testing of low power circuits and bare dies that would otherwise require expensive heat removal equipment for testing at high speeds. Three new functions, namely transition controllability, observability and test generation costs, have been defined. It has been shown that the transition test generation cost is the minimum number of transitions required to test the corresponding stuck-at fault in fanout free circuits. This cost function is used for target fault selection while the other two functions are used to guide the backtrace and objective selection procedures of PODEM. The tests generated by the proposed ATPG decrease heat dissipation during test application by a factor of 2-23 for benchmark circuits.