Multi-mode-segmented scan architecture with layout-aware scan chain routing for test data and test time reduction

In this paper, we propose a new test data compression method for reducing test data volume and test application time. The proposed method consists of two steps: scan chain compaction and dictionary-based compression scheme. The scan chain compaction provides a minimum scan chain depth by using compaction of the compatible scan cells in the scan chain. The compacted scan chain is partitioned to the multiple internal scan chains for using the fixed-length index dictionary-based compression scheme that provides the high compression ratio and the fast testing time. The proposed compression method delivers compressed patterns from the ATE to the chip and drives a large number of multiple internal scan chains using only a single ATE input and output. Experimental results for the ISCAS-89 test benches show that the test data volume and testing time for the proposed method are less than previous compression schemes.

A proposed scan chain partitioning scheme considers reduction of test set and test time, and the optimal routing inside each partitioned scan chain. First, two compatible scan cells are searched in input test set. One group of compatible scan cells is included in one partitioned scan chain, while the other group is in the other scan chain. In finding these compatible scan cells, the group-based approach is employed since it provides more optimal routing solution among the compatible scan cells in each of these two scan chains. After these two scan chains are filled with compatible scan cells, they will be able to share one of two compatible columns in input test set only during the shift-in process. Therefore, one of two compatible columns can be omitted from input test set and the scan operation. Results with ISCAS?89 benchmark circuits show that proposed method could reduce test data volume by 25-33% compared with a normal multiple scan design.

As test data continues to grow quickly, test cost also increases. For the sake of decreasing the test cost, this article presents a new data dependency compression scheme for large circuit which is based on multiple scan chains. We propose new compression architecture with fixed length for running tests. In results, when the complexity of a VLSI circuit is growing, the number of input pins for testing is very low. Since test data in power aware is not changed frequently, we use a selector to filter the unnecessary status and buffers to hold the back data. We also propose a new algorithm to assign multiple scan chains and an improved linear dependency compute method to find the hidden dependency between scan chains. Experimental results show that the proposed method can reduce both test data volume and shift-in power.

The multiple scan chain has been used in DFT (design for test) architectures primarily to reduce test application time. Since power is an emerging problem, in this paper, we present a design technique for multiple scan chains in BIST (built-in self test) to reduce average power dissipation and test application time, while maintaining the fault coverage. First, we partition the scan chain into a set of smaller chains of similar lengths in such a way that the total number of scan transitions in the scan chain is minimized. Then, we use a novel scan re-ordering algorithm in each smaller chain to further reduce the transitions. Experiments on ISCAS'89 benchmarks show up to 46.2% (average 24.4%) power reduction using the proposed technique, compared to the scan partitions given in the RTL description. Unlike previous approaches, our solution is computationally efficient and test-set independent and thus, can be effectively applied to large BIST circuitry.

Design for testability (DFT) is introduced to reduce the complexity of testing integrated circuit and help improve fault coverage. However, conventional DFT with additional 2-to-1 multiplexer (MUX) might add an increasing amount of delay and area overhead. Therefore, register transfer level (RTL) scan design is introduced to overcome this problem. This paper aims to present the development of an ASIC with RTL scan design by using multiple scan paths instead of the conventional technique, which is gate-level (GL) scan insertion to insert scan cells. This method inserts multiple scan cells by utilizing the existing multiplexer and operational units in order to reduce area overhead and delay. Besides, multiple scan paths are implemented instead of a single scan chain to reduce the complexity of the testing process, where a single scan chain has long test application times due to the high number of clock cycles for the scan chain process. RTL design is also modified by adding an extra gate for multiple scan chain insertion. The graph is derived in order to analyse the connection between registers such that the multiple scan paths can be determined accordingly. Synopsys tool is used for synthesized, placement and routing and performing automatic test pattern generation while static timing analysis is used to verify the results of the setup slack time for ASIC design. The simulation result shows that multiple scan paths insertion at RTL level has an area overhead and slack time of about 3.79% and 0.44ns less compared to multiple scan paths insertion at GL for a finite impulse response circuit with comparable high fault coverage and small delay. A comparison of the performance metrics such as area, setup slack time, and fault coverage of the multiple scan chain is done between the RTL scan and GL scan.

Scan attacks exploit facilities offered by scan chains to retrieve embedded secret data, in particular, secret keys used by the device for data encryption/decryption in mission mode. This paper presents a scan attack countermeasure based on the encryption of the data written to or read from the scan chains. The secret-key management system already embedded in the device is used to provide appropriate keys for encryption of data flowing on the scan chains. The goal of the proposed solution is to counteract the scan-related security threats while preserving test and diagnosis efficiency provided by conventional design-for-testability techniques, as well as to allow debugging capabilities in mission mode. The proposed solution can deal with both stuck-at and transition-faults test schemes as well as single and multiple scan chain configurations using test data compression schemes. We will show that the proposed scheme provides expected test/diagnostic and debug facilities as classical scan design with marginal impacts on area, test time and design flows, while successfully preventing control and observation of data flowing in the scan chains by unauthorized users.

This paper presents a multi-mode segmented scan architecture. Three operation modes are supported: broadcast, multicast, and serial. Efficient test data compression can be achieved under this architecture with limited hardware overhead. An efficient two-way partitioning algorithm is given to construct multicastmode configurations. Finally, we present a layoutaware scan chain routing for test compaction, which has not yet explored by the researchers. Experimental results show that most of the serial scan operations can be replaced by multicast operations, and thus achieve much better compression rate.

This paper proposes a scan disabling-based BIST-aided scan test (BAST) scheme. In this scheme, a pseudo-random pattern generator(PRPG) generates test vector for each slice in multiple scan chains. Using scan disabling technique, the generated test vector is shifted into the scan chains until it is compatible with its corresponding slice for a deterministic test set with don't care bits. An automatic test equipment (ATE) only needs to store the control signals instead of test data. The proposed scheme that is based on the standard scan and uses any test set with don't care bits is widely applicable and easy to deploy. Its hardware overhead that is a PRPG, phase shifter, MISR and scan disable signal is very low. Theoretical analysis and experimental results show the proposed scheme can achieve higher compression gain compared with previous low cost scheme when care bits are few.

In this paper, a novel test compression technique is proposed that can achieve very high test compression ratio with low area overhead and only one single test input. An inverter and a series of D flip-flops together with a configurable switch logic are inserted between the single input and the scan chains so as to convert the input patterns to the test data required by each scan chain. All scan chains are divided into some scan groups such that scan chains in the same group can share the same test data and the switch logic only needs to connect each group to an appropriate data provider. Hence the total area overhead is quite small. A novel algorithm is developed to determine the required test configurations and corresponding test patterns for 100% testable fault coverage. Experimental results show that on average this method can achieve data reduction factors of 23×, 124×, and 394× with 3.77%, 0.95%, and 0.03% area overhead for ISCAS'89, IWLS'05 OpenCores, and IWLS'05 Gaisler Research benchmark circuits, respectively. These results indicate that the reduction factor increases with the sizes of circuits; it even reaches 464× for a circuit containing 2.07 million gates with very small area overhead. As all test and control data can be provided by a single input, great reduction on test channel requirement is also achieved.

A combined approach for implementing system level test compression and core test scheduling to reduce SoC test costs is proposed in this paper. A broadcast scan based test compression algorithm for parallel testing of cores with multiple scan chains is used to reduce the test data of the SoC. Unlike other test compression schemes, the proposed algorithm doesn't require specialized test generation or fault simulation and is applicable with intellectual property (IP) cores. The core testing schedule with compression enabled is decided using a generalized strip packing algorithm. The hardware architecture to implement the proposed scheme is very simple. By using the combined approach, the total test data volume and test application time of the SoC is reduced to a level comparable with the test data volume and test application time of the largest core in the SoC.

In this paper, a new BIST scheme for multiple scan chain circuit is presented, where constraint input reduction, LFSR coding and folding counter are applied to compress and generate a deterministic test set. Its highlight is effectively combining previous several test methods to take full advantage of them. The new proposed scheme can't only achieve high test data compression rate, but also is compatible with traditional scan-based design flow. Experimental results show that the proposed technique needs less storage volume and significantly reduces testing time than previously published approaches. Its total test performance gains upgrade.

Dynamic power dissipation during scan-based testing of a CMOS digital circuit is reported to be a major issue of concern. The three main components of test power in scan based designs are the logic power, the sequential power and the clock power. This paper presents Integrated Scan cell and Test Vector reordering schemes for linear and non-linear (Double Tree) scan chains, with an objective to reduce the sequential test power. In this regard, it makes two important contributions: (a) It improves the scan cell reordering (SCR) algorithm proposed in Ref. [1] for the linear scan architecture. It then integrates this improved SCR algorithm with a Test Vector Reordering (TVR) strategy that results in further reduction of the sequential test power. (b) It proposes and evaluates scan cell and test vector reordering strategies for the double tree scan (DTS) architecture. It is also observed that for some classes of circuits the TVR provides more reduction of sequential test power than the SCR. Applying the proposed techniques on ISCAS benchmark circuits results in significant sequential test power reduction (with a maximum of 30% and 29.16% for linear and double tree scan architectures respectively) when compared to that output by a commercial tool.

<p>Test generation procedures for large VLSI designs are required to achieve close to 100% fault coverage using a small number of tests. They also must accommodate on-chip test compression circuits which are widely used in modern designs. To obtain test sets with small sizes one could use extra hardware such as test points or use software techniques. An important aspects impacting test generation is the number of specified positions, which facilitate the encoding of test cubes when using test compression logic. Fortuitous detection or generation of tests such that they facilitate detection of yet not targeted faults, is also an important goal for test generation procedures.</p> <p>At first, we consider the generation of compact test sets for designs using on-chip test compression logic. We introduce two new measures to guide automatic test generation procedures (ATPGs) to balance between these two contradictory requirements of fortuitous detection and number of specifications. One of the new measures is meant to facilitate detection of yet undetected faults, and the value of the measures is periodically updated. The second measure reduces the number of specified positions, which is crucial when using high compression. Additionally, we introduce a way to randomly choose between the two measures.</p> <p>We also propose an ATPG methodology tailored for BIST ready designs with X-bounding logic and test points. X-bounding and test points used to have a significant impact on test data compression by reducing the number of specified positions. We propose a new ATPG guidance mechanism that balances between reduced specifications in BIST ready designs, and also facilitates detection of undetected faults. We also found that compact test generation for BIST ready designs is influenced by the order in which faults are targeted, and we proposed a new fault ordering technique based on fault location in a FFR. Transition faults are difficult to test and often result in longer test lengths, we propose a new fault ordering technique based on test enumeration, this ordering technique and a new guidance approach was also proposed for transition faults. Test set sizes were reduced significantly for both stuck-at and transition fault models.</p> <p>In addition to reducing data volume, test time, and test pin counts, the test compression schemes have been used successfully to limit test power dissipation. Indisputably, toggling of scan cells in scan chains that are universally used to facilitate testing of industrial designs can consume much more power than a circuit is rated for. Balancing test set sizes against the power consumption in a given design is therefore a challenge. We propose a new Design for Test (DFT) scheme that deploys an on-chip power-aware test data decompressor, the corresponding test cube encoding method, and a compression-constrained ATPG that allows loading scan chains with patterns having low transition counts, while encoding a significant number of specified bits produced</p> <p>by ATPG in a compression-friendly manner. Moreover, the new scheme avoids periods of elevated toggling in scan chains and reduces scan unload switching activity due to unique test stimuli produced by the new technique, leading to a significantly reduced power envelope for the entire circuit under test.</p>

A test pattern compression scheme for test data volume and application time reduction is proposed. While compression reduces test data volume, the increased number of internal scan chains due to an on-chip, fixed-rate decompressor reduces test application time proportionately. Through on-chip decompression, both the number of virtual scan chains visible to the ATE and the functionality of the ATE are retained intact. Complete fault coverage is guaranteed by constructing the decompression hardware deterministically through analysis of the test pattern set.

Low power design techniques have been employed for more than two decades, however an emerging problem is satisfying the test power constraints for avoiding destructive test and improving the yield. Scan architectures represent the most used approach for testing digital integrated circuits. While several methods have been proposed for reducing the power dissipation due to scan shifting, very little work has been done towards reducing the power dissipation during the capture cycles. This paper proposes a method of transforming a typical scan architecture for reducing the power dissipation during both the shifting cycle and the capture cycle. The basic idea is to split the the scan chain into multiple length-balanced partitions and to enable only one partition at each test clock. This way, instead of having all the scan cells active at the same time, only a fraction of them will be active in each test clock cycle, which will reduce substantially the power dissipation in the circuit under test. Unlike previously proposed methods for shifting power reduction based on scan chain partitioning which use a single capture clock per test cycle, our approach uses multiple capture clocks per test cycle, which allows enabling only a fraction of the scan chain during each shift or capture clock, thus reducing the switching activity in the circuit under test not only during shifting but also during capture. Therefore, the proposed method represents an unified solution for reducing both shifting and capture power dissipation during scan-based test. The proposed method also allows full reuse of the test vectors of the original scan architecture.