Multiple Single Input Change Vectors for Built-In Self Test (MSIC-BIST)

This paper introduces a test pattern generator (TPG) in order to use in built-in self-test(BIST). MSIC TPG generates multiple single input change (MSIC) vectors in a pattern, i.e., each vector applied to a scan chain is an SIC vector. With the help of reconfigurable Johnson counter and a scalable SIC counter its easy to generate a class of minimum transition sequences. The proposed TPG is flexible to test-per-scan schemes. A theory is developed to represent and analyze the sequences and to extract a class of MSIC sequences. Analysis results show that the produced MSIC sequences have the favorable features of uniform distribution, minimum transitions, and low input transition density. The Performances of the designed MSIC TPG and the circuit under test are evaluated. Simulation results shows that it can save delay time and power. It also achieves the target fault coverage without increasing the test length.

This paper proposes a novel test pattern generator (TPG) for built-in self-test. Our method generates multiple single-input change (MSIC) vectors in a pattern, i.e., each vector applied to a scan chain is an SIC vector. A reconfigurable Johnson counter and a scalable SIC counter are developed to generate a class of minimum transition sequences. The proposed TPG is flexible to both the test-per-clock and the test-per-scan schemes. A theory is also developed to represent and analyze the sequences and to extract a class of MSIC sequences. Analysis results show that the produced MSIC sequences have the favorable features of uniform distribution and low input transition density. The performances of the designed TPGs and the circuits under test with 45 nm are evaluated. Simulation results with ISCAS benchmarks demonstrate that MSIC can save test power and impose no more than 7.5% overhead for a scan design. It also achieves the target fault coverage without increasing the test length.

Single input change (SIC) test sequence has been investigated in recent years because it is effective to reduce the test power consumption. Deterministic built-in self-test (BIST) can achieve the high fault coverage with relatively short test application time and low test cost. In this paper, seeds selection scheme of SIC sequences based on deterministic ATPG test patterns is proposed for decreasing the test power consumption and test application time with high test fault coverage. Proper selection of SIC seeds is the key aspect to a successful low power deterministic BIST technique. Furthermore, simulated annealing algorithm is used to optimize the numbers of seeds. A simple hardware structure can implement the generation of SIC sequences. Experimental results based on ISCAS'85 benchmark circuits demonstrate that the proposed algorithm can reduce the number of SIC seeds. Test application time and average power can be decreased, and test fault coverage also keep high compared to random SIC (RSIC) test sequences.

The main challenging areas in VLSI design are performance, cost, testing, area, reliability and power. The demand for portable computing devices and communication system are increasing rapidly. The power dissipation during test mode is much more than in normal mode. Hence it is important to optimize power during testing. BIST is a Design for Testability (DFT) technique, because it makes the electrical testing of a chip easier, faster, more efficient, and less costly. Hence the low power Multiple Single Input Change (MSIC) test patterns are generated for BIST based schemes. The characteristics of these multiple single input change patterns are minimum transition, uniform distribution and uniqueness of patterns. A reconfigurable Johnson counter, XOR array and a seed generator are used for generating test patterns. The seed generator is a linear feedback shift register. A single seed or multiple seeds can be used which will affect the number of patterns generated. Since the patterns are of low transitions, the power dissipation during test mode can be reduced. Here the generated patterns are given to different scan chains. To reduce the hardware overhead, delay and power consumption an accumulator based circuit can be used. The generated patterns are applied to the s344 benchmark circuit for fault injection and fault detection. The coding is done in VHDL and is simulated in XILINX ISE simulator.

A novel design of a test pattern generator (TPG) for built-in self-testing (BIST) of path delay faults, is proposed. For an n-input CUT, the TPG generates a sequence of length (n.2/sup n/+1), that includes all n.2/sup n/ single-input-change (SIC) test pairs, and hence optimal. The generation of such a sequence of minimum length (i.e., n.2/sup n/+1) was an open problem. A simple iterative circuit of the TPG is then constructed. This provides minimum test application time for testing path delay faults, and compares favorably with the earlier BIST designs.

The ever increasing size and complexity of today’s Very-Large-Scale-Integration (VLSI) designs requires a thorough investigation of new approaches for the generation of test patterns for both test and diagnosis of faults. SAT-based automatic test pattern generation (ATPG) is one of the most popular methods, where, in contrast to classical structural ATPG methods, first a mathematical representation of the problem in form of a Boolean formula is generated, which is then evaluated by a specialized solver. If the considered fault is testable, the solver will return a satisfying assignment, from which a test pattern can be extracted; otherwise no such assignment can exist. In order to speed up test pattern generation, the concept of D-chains was introduced by several researchers. Thereby supplementary clauses are added to the Boolean formula, reducing the search space and guiding the solver toward the solution. In the past, different variants of D-chains have been developed, such as the backward D-chain or the indirect D-chain. In this work we perform a thorough analysis and evaluation of the D-chain variants for test pattern generation and also analyze the impact of different D-chain encodings on diagnostic test pattern generation. Our experimental results show that depending on the incorporated D-chain the runtime can be reduced tremendously.

DFT (Design for Testability) is a methodology of testing for manufacturing defects in a chip. DFT consists of scan, ATPG (Automatic test pattern generation) methodologies and the BIST (Built in self-test) methods. This paper explores ATPG for pattern generation and LBIST (Logic built-in self-test) for testing. LBIST is explored and tested using pseudorandom test pattern generation. The fault list created for undetected faults are dumped into ATPG and fault specific test patterns are generated. These patterns detect the random pattern resistant faults (which are undetected by pseudorandom testing patterns). Further, a smart compression algorithm is defined to compress the pattern which can be stored inside the chip for LBIST testing, with no added memory overhead, and the minimum extra hardware (which only comprises of combinational logic). The proposed algorithm has been reviewed and analyzed and it has been found that the fault coverage achieved is 86.01%.

Single input change (SIC) sequence for VLSI testing has been researched because of effectiveness to more test fault models and low power consumption testing. It is the high fault coverage in deterministic built-in self-test (BIST) with low test cost and short test application time. The sequential single input change (SSIC) sequence used in deterministic BIST is presented in this paper for decreasing the dynamic power, reducing test application time and increasing fault coverage. The selection of seed vectors is the significant technique in deterministic BIST. The critical features of SSIC sequence are proposed for selecting seed vectors. The SSIC sequence generator is designed. The simulation results using benchmark circuits show that the SSIC sequences can increase fault coverage and decrease application time than random SIC sequences. SSIC sequence also has low dynamic power consumption.

Today, VLSI design has progressed to a stage where it needs to incorporate methods of testing circuits. The Automatic Test Pattern Generation (ATPG) is a very attractive method and feasible on almost any combinational and sequential circuit. Currently available automatic test pattern generators (ATPGs) generate test sets that may be excessively long. Because a cost of testing depends on the test length, compaction techniques have been used to reduce that length. The motivation for studying test compaction is twofold. Firstly, by reducing the test sequence length, the memory requirements during the test application and the test application time are reduced. Secondly, the extent of test compaction possible for deterministic test sequences indicates that test pattern generators spend a significant amount of time generating test vectors that are not necessary. The compacted test sequences provide a target for more efficient deterministic test generators. Two types of compaction techniques exist: dynamic and static. The dynamic test sequence compaction performs compaction concurrently with the test generation process and often requires modification of the test generator. The static test sequence compaction is done in a post-processing step to the test generation and is independent of the test generation algorithm and process. In the thesis, a new idea for static compaction of test sequences for synchronous sequential circuits has been proposed. Our new method - SUSEM (Set Up Sequence Elimination Method) uses the circuit state information to eliminate some setup sequences for the target faults and consequently reduce the test sequence length. The technique has been used for the test sequences generated by HITEC test generator. ISCAS89 benchmark circuits were used in our experiments, for some circuits which have a large number of target faults and relatively small number of flip-flops, the very significant compactions have been obtained. The more important is that this method can be used to improve the test generation procedure unlike most static compaction methods which blindly or randomly remove parts of test vectors and cannot be used to improve the test generators.

Test pattern generation using thermometer code counter in TPC technique for BIST implementation

Design for low power testing is primary concern in modern VLSI circuits. In this paper a novel test pattern generator (TPG) is proposed which is more suitable for built in self test (BIST) architecture, used for testing of VLSI circuits. The objective of the BIST is to reduce power consumption during testing of VLSI circuits. In CMOS devices 80% of power consumption is due to switching activity occurred during operation. The proposed TPG is based on read only memory (ROM) which is carefully designed to store the test vectors with minimum area over the conventional ROM. This reduces the number of CMOS transistors significantly when compared to that of LFSR/counter TPG. The proposed TPG is more suitable for deterministic pattern testing and the fault coverage is improved over the LFSR. Low power reordered test patterns also can also be stored in the same order to reduce the test power in circuit under test (CUT). The TPG is designed and implemented for benchmark circuits ISCAS 85 and 89. Experimental results shows that a considerable reduction in number of CMOS devices and test power is achieved over the LFSR-TPG

For current VLSI designs, there are two kinds of well-accepted digital testing technologies. One is for embedded memories and the other is for the logic. For embedded memories, Built-In-Self-Test (BIST) is used. For the logic, the main solutions are based on scan DFT and automatic test pattern generation (ATPG). However, to reduce the need to use an external tester, and to ease test reuse at the system level, more designs are using BIST to test logic. In the future, with system on chip (SoC) requirements and deep Sub-Micron (DSM) technologies, we believe that BIST and scan-based ATPG will continue to be the main solutions to VLSI testing. However, to be successful, some improvements are needed. The author discusses future trends in three categories: test quality, test application cost and test development effort.

This paper proposes a methodology to generate the multiple test patterns varying in single bit position for built-in-self-test (BIST). The traditional patterns which were generated using Linear feedback shift registers lack correlation between consecutive test vectors. So, in order to improve correlation between the subsequent test vectors, the patterns were produced using Gray counter and Decoder. The Area optimization is achieved by reducing the total number of gate count to implement the design. In order to optimize the power, the number of toggles between the subsequent test vectors is curtailed. The generated test patterns have an advantage of minimum transition sequence. Simulation results on multiplier circuit shows a reduction of 54% in area overhead and 12% in power overhead compared to pattern generation using Reconfigurable Johnson counter and LFSR. 100% fault coverage is achieved while generating patterns using gray counter, decoder and accumulator architecture. Time coverage is same as time required for generating patterns using existing methodology. The methodology for producing the test vectors for BIST is coded using VHDL and simulations were performed with ModelSim 10.0b. The Area utilization and the power report were obtained with the help of Xilinx ISE 9.1 software.

A new technique called input reduction is proposed for built-in self test (BIST) test pattern generator (TPG) design and test set compaction. This technique analyzes the circuit function and identifies sets of compatible and inversely compatible inputs; inputs in each set can be combined into a test signal in the test mode without sacrificing fault coverage, even if they belong to the same circuit cone. The test signals are used to design BIST TPGs that guarantee the detection of all detectable stuck-at faults in practical test lengths. A deterministic test set generated for the reduced circuit obtained by combining inputs into test signals is usually more compact than that generated for the original circuit. Experimental results show that BIST TPGs based on input reduction achieve complete stuck-at fault coverage in practical test lengths (/spl les/2/sup 30/) for many benchmark circuits. These are achieved with low area overhead and performance penalty to the circuit under test. Results also show that the memory storage and test application time for external testing using deterministic test sets can be reduced by as much as 85%.

Shrinking power budgets in low power system-on-chips (SoCs) have elevated test power consumption as a major consideration for chip design and test engineering teams. Many traditional automatic test pattern generation (ATPG) and design-for-test (DFT) techniques for test power reduction are either effective for circuits not using test data compression hardware or have implications on the physical design cycle. This paper describes a technique for reducing peak current during scan based testing that can work in the presence of compression, and impose no restrictions on physical design, e.g. related to chip clocking. We propose low-design effort modifications to the test compression logic (wrapper-like changes) that enable us to (a) bypass scan chains or groups of them and (b) shift in constant values into the bypassed flip-flops for lowering the instantaneous current drawn. The modifications are easily localized to a scan chain wrapper that can be used with any scan compression solution. An SoC using low-power scan chain wrappers provides sufficient configurability (scan chains bypassed or scan chains included) to explore different power reductions with test cost trade-offs. We describe a methodology that allows us to manage the inherent configurability available in our solution. For empirical validation, we have implemented low-power scan chain wrappers for a subset of scan chains in a recently taped-out 65nm low-power SoC. We present experimental data from ATPG and initial silicon power measurements for this chip to demonstrate the benefits and limitations of the proposal.