Design For Testability Approach Research Articles

Fault simulation for design for testability inserted designs

<p>Systematic design for testability (DFT) is a technique to enhance the testability of design so that it is further organized and self-regulating. The objective of systematic DFT is to enhance a circuit's operability and evidence. This can be performed in a variety of ways. The scan pattern method is the extremely predominant, and it modifies the design's internal sequential circuitry. In this manuscript, frequently used industry standard functional register-transfer level (RTL) designs are chosen. Structured DFT approach is adopted to do scan insertion and automatic test pattern generation (ATPG) to enhance the testability. Proposed methodology provides the controllability and observability for the clocks and reset used in chosen RTL designs by eliminating S rule and D rule violations by adding test logic. Also able to insert stuck at faults and achieve fault coverage of 97.78% and test coverage of 99.26% for DFT architecture for Wallace tree multiplier design, and found different classes of faults as testable and untestable faults and also performed fault simulation for the intended designs to detect fault from the created deterministic patterns.</p>

Invisible-Scan: A Design-for-Testability Approach for Functional Test Sequences

Functional test sequences can detect defects that are not detected by scan-based tests, but overall, achieve a lower gate-level fault coverage than scan-based tests. Design-for-testability (DFT) approaches for functional test sequences cause the sequences to deviate from functional operation conditions in arbitrary ways over the entire design. This paper introduces the concept of invisible-DFT as a DFT approach for functional test sequences, where the effects of activating the DFT logic are confined to selected logic blocks. This paper develops an invisible-scan approach. Considering a single logic block, the procedure described in this paper inserts scan shift cycles into a functional test sequence while maintaining the same primary input and output sequences for the logic block. This makes the activation of the DFT logic invisible to other logic blocks. The procedure allows a limited number of primary output vectors to be corrected for this purpose. Experimental results are presented to demonstrate the increase in fault coverage that can be achieved by invisible-scan.

IJARCCE - Computer and Communication Engineering

This paper presents an error detection and data recovery (EDDR) design, based on the residue-and-quotient (RQ) code, to embed into motion estimation (ME) for video coding testing applications. An error in processing elements (PEs), i.e. key components of a ME, can be detected and recovered effectively by using the EDDR design. The proposed EDDR design for ME testing can detect errors and recover data with an acceptable area overhead and timing penalty. The functional verification and synthesis can be done by Xilinx ISE. That is when compare to the existing design the implemented design area and timing will be reduced.. The new Joint Video Team (JVT) video coding standard has garnered increased attention recently. Generally, motion estimation computing array (MECA) performs up to 50% of computations in the entire video coding system, and is typically considered the computationally most important part of video coding systems. Thus, integrating the MECA into a system-on-chip (SOC) design has become increasingly important for video coding applications. Although advances in VLSI technology allow integration of a large number of processing elements (PEs) in an MECA into an SOC, this increases the logic- per-pin ratio, thereby significantly decreasing the efficiency of chip logic testing. For a commercial chip, a video coding system must introduce design for testability (DFT), especially in an MECA. The objective of DFT is to increase the ease with which a device can be tested to guarantee high system reliability. Many DFT approaches have been developed. These approaches can be divided into three categories: ad hoc (problem oriented), structured, and built-in self-test (BIST). Among these techniques, BIST has an obvious advantage in that expensive test equipment is not needed and tests are low cost.

A design for testability approach for nano-CMOS analogue integrated circuits

Dependability requirements must be considered from the beginning when designing safety-critical systems. Therefore, testing should even be considered earlier, intertwined with the design process. The process of designing for better testability is called design for testability (DfT). This article presents two designs for testability and fault diagnosis techniques using a new design analogue checker circuit in order to improve the testability and the diagnosability of nano-CMOS (complementary metal oxide semiconductor) analogue circuits used in safety-critical applications based on the system-on-chip (SoC) approach design. The testing techniques presented in this work can be done during and after the system fabrication. The checker is implemented in full-custom 65 nm Complementary metal–oxide–semiconductor (CMOS) technology with low supply voltage and small-size capabilities. SPICE simulations of the post-layout extracted CMOS checker, which include all parasitic, are used to validate the technique and demonstrate the acceptable electrical behaviour of the checker.

Multiband RF-sampling receiver front-end with on-chip testability in 0.13 μm CMOS

In this paper a flexible RF-sampling front-end primarily intended for WLAN standards operating in the 2.4 GHz and 5-6 GHz bands is presented. The circuit is implemented with on-chip Design for Test (DfT) features in 0.13 µm CMOS process. The front-end consists of a wideband LNA, a sampling IQ down-converter implemented as switched-capacitor decimation filter, test attenuator (TA), and RF detectors. The architecture is generic and scalable in frequency. It can operate at a sampling frequency up to 3 GHz and RF carrier up to 6 GHz with 2× subsampling. The selectable decimation factor of 8 or 16 makes the A/D conversion feasible. The frequency response, linearity, and NF of the whole front-end have been measured. The power consumption of complete RF front-end is 176 mW. The on-chip DfT features are helpful in reduction of overall test cost and time in volume production. The measurement results show the feasibility of DfT approach for multiband radio receiver design using standard CMOS process.

Satisfiability-Based Automatic Test Program Generation and Design for Testability for Microprocessors

In this paper, we present a satisfiability (SAT)-based framework for automatically generating test programs that target gate-level stuck-at faults in microprocessors. The microarchitectural description of a processor is first translated into a unified register-transfer level (RTL) circuit description, called assignment decision diagram (ADD), for test analysis. Test generation involves extraction of justification/propagation paths in the unified circuit representation from an embedded module's input-output (I/O) ports to primary I/O ports, abstraction of RTL modules in the justification/propagation paths, and translation of these paths into Boolean clauses in conjunctive normal form (CNF). Additional clauses are added that capture precomputed test vectors/responses at the embedded module's I/O ports. An SAT solver is then invoked to find valid paths that justify the precomputed vectors to primary input ports and propagate the good/faulty responses to primary output ports. Since the ADD is derived directly from a microarchitectural description, the generated test sequences correspond to a test program. If a given SAT instance is not satisfiable, then Boolean implications (also known as the unsatisfiable segment) that are responsible for unsatisfiability are efficiently and accurately identified. We show that adding design for testability (DFT) elements is equivalent to modifying these clauses such that the unsatisfiable segment becomes satisfiable. Test generation at the RTL also imposes a large number of initial conditions that need to be satisfied for successful detection of targeted stuck-at faults. We demonstrate that application of the Boolean constraint propagation (BCP) engine in SAT solvers propagates these conditions leading to significant pruning of the sequential search space which in turn leads to a reduction in test generation time. Experimental results demonstrate an 11.1X speedup in test generation time for test generation at the RTL over a state-of-the-art gate-level sequential generator called MIX, at comparable fault coverages. An unsatisifiability-based DFT approach at the RTL improves this fault coverage to near 100% and incurs very low area overhead (3.1%). Unlike previous approaches that either generate a test program consisting of random instruction sequences or assume the existence of test program templates, the proposed approach constructs test programs in a deterministic fashion from the microarchitectural description of a processor

Detection of Delay Faults in Memory Address Decoders

In this paper we present an efficient test concept for detection of delay faults in memory address decoders based on the march test tactic. The proposed Transition Sequence Generator (TSG) generates an optimal transition sequence for sensitization of the delay faults in address decoders by Hayes's transformation on a reflected Gray code. It can be used for parallel Built-In Self-Testing (BIST) of high-density RAMs. We also present an efficient Design For Test (DFT) approach for immediate detection of the effects of the delay faults in the address decoders which does not change memory access time. It requires extra logic to be attached to the outputs of the address decoders. This DFT approach can be used to increase memory testability for both on-line and off-line testing of single- and multi-port RAMs.

Design for Testability Using State Distances

The average distance between states is proposed as a new testability measure for finite state machines (FSMs). Also proposed is the concept of center state to reduce distances in FSMs. This test function embedding technique has been shown to improve the testability of sequential circuits with minimal overhead. An overview of several design-for-testability (DFT) and synthesis-for-testability (SFT) methods for sequential circuits will also be given in this paper. Experimental results have shown that the DFT approach is more advantageous than the SFT approach to implement our test function. The contribution of this paper is to analyze the trade-offs between several aspects of DFT and SFT techniques.

Nonscan design-for-testability techniques using RT-level design information

This paper presents nonscan design-for-testability (DFT) techniques applicable to register-transfer (RT)-level data path circuits. Knowledge of high-level design information, in the form of the RT-level structure, as well as the functions of the RT-level components is utilized to develop effective nonscan DFT techniques. Instead of conventional techniques of selecting flip-flops (FF's) to make systems controllable/observable, execution units (EXU's) are selected using the EXU S-graph introduced in this paper. Controllability/observability points can be implemented using register files and constants. We introduce the notion of k-level controllable and observable loops and demonstrate that it suffices to make all the loops k-level controllable/observable, k>0, to achieve very high test efficiency. The new testability measure eliminates the need by traditional DFT techniques to make all loops directly (zero-level) controllable/observable, reducing significantly the hardware overhead required and making the nonscan DFT approach feasible and effective. We discuss ways of avoiding the formation of reconvergent regions while adding test points to make loops k-level controllable/observable. We introduce dual points, which utilize the different controllability/observability levels of loops, to make one loop controllable while making another loop observable. We present efficient algorithms to add the minimal hardware possible to make all loops in the data path k-level controllable/observable, without the use of scan FF's. The nonscan DFT techniques were applied to several data path circuits. The experimental results demonstrate the effectiveness of the k-level testability measure, and the use of distributed and dual points, to generate easily testable data paths with reduced hardware overhead. The hardware overhead and the test application time required for the nonscan designs are significantly lower than for the partial scan designs. Most significantly, the experimental results demonstrate the ability of the RT-level DFT techniques to produce nonscan testable data paths, which can be tested at-speed.

Fault Modeling of ECL for High Fault Coverage of Physical Defects

Bipolar Emitter Coupled Logic (ECL) devices can now be fabricated at higher densities and consumes much lower power. Behaviour of simple and complex ECL gates are examined in the presence of physical faults. The effectiveness of the classical stuck-at model in representing physical failures in ECL gates is examined. It is shown that the conventional stuck-at fault model cannot represent a majority of circuit level faults. A new augmented stuck-at fault model is presented which provides a significantly higher coverage of physical failures. The model may be applicable to other logic families that use logic gates with both true and complementary outputs. A design for testability approach is suggested for on-line detection of certain error conditions occurring in gates with true and complementary outputs which is a normal implementation for ECL devices.

Generic DFT approach for pattern sensitive faults in word-oriented memories

The testability problem of word-oriented memories (WOMs) for pattern sensitive faults is addressed. A novel design for testability (DFT) strategy allows efficient built-in self-testing (BIST) of WOMs. By proper selection of the memory array tiling scheme, it is possible to implement O(√n) BIST algorithms which test WOMs for various types of neighbourhood pattern sensitive faults (NPSFs). The inputs of the column decoders are modified to allow parallel writing into multiple words, and coincidence comparators are added to allow parallel verification of row data with minimal effect on chip area and performance.

Self-testing approaches for VLSI arrays

A self-testing method which is applicable 1- and 2-dimensional arrays, is presented. The method is based on a state-table-verification approach and a criterion referred to as GI (group identical) testability. GI testability is an extension and modification of PI (partition identical) testability and it is used to simplify response verification for self-testing. It is shown that the response verifier for PI testability does not always detect all faults and a new response verifier for GI-testable arrays is proposed. CGI-testable arrays which are simultaneously C and GI testable, are analysed. It is proved that a C-testable 1-dimensional array with n cells is GI testable if n>or=2T, where T is the least common multiple of the test sequences for verifying a cell in the array. Design for testability approaches for unilateral and bilateral arrays are proposed, and similar conditions are developed for 2-dimensional arrays. Methods for reducing the size of CGI-testable unilateral and bilateral arrays are discussed.

Automated Bist for Regular Structures Embedded in Asic Devices

Testing complex very large-scale integrated (VLSI) circuits is increasingly difficult. It is almost impossible to achieve high fault coverages without using design for testability (DFT) approaches. In one of the most promising DFT approaches, the complex VLSI circuit is divided into various structural modules, and an appropriate built-in self-test (BIST) scheme for each module is then implemented. This approach also provides a path to board- and system-level test. This paper presents a general procedure to implement BIST for a specific set of modules, i.e., embedded regular structures such as static random-access memory (SRAM), read-only memory (ROM), and register files. We will show that fault coverages achieved with this procedure are greater than 99 percent, because the deterministic BIST algorithms and output-data compaction techniques adopted are structure-specific. Moreover, fault simulations are not needed because the fault coverages are analytically determined by an algorithmic approach. The general procedure presented here results in an automated BIST implementation. An illustration of such a procedure is presented through the BIST register file example.

On inherent untestability of unaugmented microprogrammed control

Effective and efficient testing of the control part of a processor has remained a difficult problem. While several approaches have been proposed in the literature for handling unaugmented control parts, they involve questionable assumptions, and the results have not been encouraging. Here it is shown that unless some DFT (Design for Testability) approaches are taken, microprogrammed control is inherently a poorly testable structure. The considerations include lack of an elegant fault model, presence of components with low random testability, the length of a checking sequence and information-theoretic considerations. The design approaches must therefore include DFT augmentations and/or removal of sub-functional logic.