A multi-mode scannable memory element for high test application efficiency and delay testing

This paper introduces a new multi-mode scannable memory element which allows pseudorandom testing to be integrated with scan in sequential circuits without the need of any design changes. As in the case of scan, the new element is used in place of regular flip-flops in the design library. Concurrent with normal operation, the design can accumulate a signature of the state variables in the scan-register configured as a multiple input signature analyzer (MISA). Thus virtually complete state observability is achieved without the need of scanning-out the state for each test-input. The pseudorandom states of the MISA can also be utilized as state inputs in pseudorandom testing. In this way, most faults are covered in a pseudorandom, “test per clock” mode. Only a few random pattern resistant faults require scan, greatly reducing test application time. Pseudorandom delay testing of the true normally active circuit paths is also possible. Two-pattern tests are supported. Finally, we show that the new memory element can also be used for fault-tolerant design.

Built-in self test (BIST) techniques are widely used in today's complex integrated circuits, since they employ on-chip test pattern generation and response verification. Arithmetic BIST techniques utilize modules that commonly exist in datapath modules (accumulators, counters etc.). In order to perform the test generation and response verification operations. In order to detect sequential faults that occur into current CMOS circuits, two-pattern tests are required. Furthermore, delay testing, commonly used to assure correct temporal circuit operation at clock speed, requires two-pattern tests. In this paper a novel algorithm for the generation of two-pattern tests is presented. The presented algorithm utilizes modules included in datapath circuitry to generate two-pattern tests; its implementation in hardware compares favorably with techniques that have been presented in the open literature

~ NJ 07974 Abstract - This paper addresses the problem of simukating transition faults in synchronous sequential circuits. After presenting the concept of the transition fault modell for sequential circuits, we present a fault simulation algorithm for transition faults. The algorithm is a modification of PROOFS, a parallel, differential fault simulation algorithm for stuck faults. A novel fault injection technique is pro- posed. Experimental results show that neither a comprehen- sive functional verification sequence nor a test sequence gen- erated by a sequential circuit test generator for stucck-at faults produces a high fault coverage for transition faults. and finite state machine (FSM) synthesis for delay testabil- ity was adtlressedl. A known reset state is required. The method has limited capability of handling large circuits, because it Icquires the extraction of the complete or partial state transition graph. The approach suggested in 1131 assumes that the circuit is fault-free in the initialization and fault propagation phases. This suggestion is valid if the clock is applied alt a lower speed during the initialization and the fault propagation phases and is applied at a rated speed during the fault activation phase. Slow clock for ini- tialization ,and fault propagation is also assumed in (12). To the author's Icnowledge, no delay-fault simulator €or sequential circuits has been reported before. In this paper, we address the problem of simulating transition faults in sequential circuits. We first enhance the transition fault model for the gate-delay faults and the stuck-open faults in synchronous sequential circuits. We assume the input vectors and clock are applied at speed and at a fixed interval during test application. The primary outputs are: also observed at a fixed interval. We use a transition fault of size n clock cycles to model the defects that cause im extra delay of n clock cycles to a transition. We present a fault simulation algorithm for the proposed fault model. Fault simulation results on the ISCAS-89 sequential benchmark circuits are presented in Section 5.

A methodology for the redesign of sequential VLSI circuits to increase the circuit speed involves cascading the circuit over a plurality of time frames without the memory elements, identifying any long false paths in the cascaded circuit, reconfiguring the original circuit to eliminate the false paths while providing fanout to preserve functionality, and retiming the reconfigured circuit to reduce circuit delay.

Testing for delay and CMOS stuck-open faults requires two pattern tests and test sets are usually large. Built-in self-test (BIST) schemes are attractive for such comprehensive testing. The BIST test pattern generators (TPGs) for such testing should be designed to ensure high pattern-pair coverage. In this paper, necessary and sufficient conditions to ensure complete/maximal pattern-pair coverage for linear feedback shift register (LFSR) and cellular automata (CA) have been derived. The theory developed here identifies all LFSR/CA TPGs which maximize pattern-pair coverage under any given TPG size constraints. It is shown that LFSRs with primitive feedback polynomials with large number of terms are better for two-pattern testing. Also, CA are shown to be better TPGs than LFSRs for two-pattern testing. Results derived in this paper provide practical algorithms for the design of optimal TPGs for two-pattern testing. Experiments on some benchmark circuits indicate the TPGs designed using the procedures outlined in this paper provide much higher delay fault coverage than other TPGs. >

The ternary T-gate can be used as a basic building block to construct both combinational and sequential circuits. Since the T-gate is one kind of tree-type universal logic module, any combinational circuit can be built up with modular logic arrays. For constructing ternary memory elements, however, the T-gate is required to be static hazard-free. A theoretical study is done on the necessary conditions for the practical realization of the static-hazard-free T-gate. On the basis of the result obtained, the static-hazard-free T-gate is realized using the ECL technique. The static-hazard-free T-gates obtained here can be used as building blocks to construct memory elements. Various memory elements such as D flip-flap-flop (FFF), D master-slave FFF, B master-slave FFF, and counting FFF is constructed easily. Using these memory elements, three different types of ternary counters can be designed and realized. They are an asynchronous signed ternary counter, a synchronous signed ternary counter, and a counter based on a shift register. Their design methods are discussed. These ternary counters are superior to the binary ones in that the up-down cotnting can easily be carried out by one input signal.

A general and unified theory of the kinematic relationships in bulge tests

Safety-critical systems used in applications that demand high levels of dependability, efficiency, and fault-tolerance often use sequential logic circuits in its design and implementation. The safety-critical digital system typically uses latches, flip-flops, and other memory elements, which are prone to the effects of natural faults and single event upsets (SEUs) caused by radiation-induced effects. The faults can lead to subsystem failures due to the continuous advancement in the realization of the small size transistor. To design a reliable digital-based system, it is essential to develop new fault-tolerance approaches that are integrated into the design of sequential logic circuits. This work proposes a novel fault-tolerant approach based on the redundancy of sequential logic circuit, which consists of a variety of design components, D flip-flop storage elements linked to a fault injection unit, a duplicate modular redundancy, and data monitoring units with a switching circuit. The experimental simulation results using a five-state Markov chain analysis model prove that the proposed fault-tolerant system can achieve 0.99999998 for reliability of the fault detection coverage (C) which equal to 0.99999. Finally, we believe that using this new approach of fault-tolerance and redundancy would improve the dependability and reliability of next generation safety-critical applications.

The objective of our research is to study concepts and designs of 21st century libraries, which provide a new approach to supporting lifelong learning and diverse learning experiences and from this, develop design guidelines for transitioning interior spaces of a traditional university library into a 21st century library. The Pridi Banomyong Library, located at Thammasat University, Tha Phra Chan Campus, Thailand, was selected as the specific case study for this research in modernizing an outdated 20st century library. The Pridi Banomyong Library was built in 1994 on the occasion of Thammasat University’s 60th anniversary and is nationally renowned in the field of Social Sciences. The research process includes conducting surveys and collecting data on the project site, studying the ideas, theories, and evolution of library design, conducting interviews and seeking opinions from directors, staff, and library users, analyzing and summarizing the current library usage and future needs, proposing new interior concepts and layouts, and providing comparative data on design concepts to summarize a design guideline for modernizing the library. These design concepts incorporate the expression of the library’s vision, mission, and identity within the context of learning in the 21st century and, in particular, support lifelong learning and diverse learning experiences through socially oriented learning spaces and various media. The design also proposes a new identity for the library with a focus on digital technology, positioning the library users as the central focus, and further enhancing the learning experience by highlighting the historical significance and value of the building and its location. In conclusion, this research and design revealed that the concept of 21st century skills has resulted in a major change in library design. By promoting new skills, such as interactive learning, social activities, lifelong learning, and diverse learning experiences, the Pridi Banomyong Library will serve as a center of Thammasat University for lifelong and social learning. The library is an exemplar design case for other libraries throughout Thailand that will help to develop Thai society into a more learning-centered society.

The author presents a method for generating test sequences to detect delay faults in sequential circuits using the stuck-at-fault sequential test generator STALLION. The method is complete in that it will generate a delay test sequence for a targeted fault given sufficient CPU time, if such a sequence exists. Faults for which no delay test sequence exists are termed sequentially delay redundant. The author describes means of eliminating sequential delay redundancies in logic circuits. He presents a partial-scan methodology for enhancing the testability of difficult-to-test or untestable sequential circuits, wherein a small number of flip-flops are selected and made controllable/observable. The selection process guarantees the elimination of all sequential delay redundancies. It is shown that an intimate relationship exists between state assignment and delay testability of a sequential machine. A state assignment algorithm for the synthesis of sequential machines with maximal delay fault testability is described. Preliminary experimental results using the test generation, partial-scan, and synthesis algorithms are presented. >

Existing delay test generation techniques focus on test generation for combinational blocks, and assume the inputs and outputs of the block to be unconstrained. Test application for delay tests is done by means of enhanced scan, scan shifting or functional justification; all these techniques impose minimal constraints on the inputs and the outputs of the combinational block targeted. This leads to over-testing the components for delay defects. This paper analyzes the gains associated with determining the multi-cycle (sequential) sensitization of delay tests. The advantages of determining multi-cycle sensitization is then illustrated on benchmark designs with and without a delay-specific fault model.

The power of digital electronics stems from its ability to provide and use memory elements. Instead of output signals being dependent only on the present state of the inputs they can be made dependent on the history of inputs applied to the circuit. A simple example shows the difference between these two operating conditions. With combinational logic the only possible outputs from one input (X) are 0, 1, X and X, and only X requires the intervention of any electronics. One possibility for a circuit with memory is for the outputs to register the number of times a single input has changed from 0 to 1, i.e. count the number of input pulses. With 10 outputs 1024 (210) different output states are possible, and, if a binary representation is chosen, the circuit can count from 0 to 1023. To obtain a larger counting range, the circuit needs changing to provide more outputs but no change is required to the number of inputs. Circuits containing combinational and memory elements are known as sequential circuits.

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.

Single event upset mitigation by means of a sequential circuit state freeze

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.