Transition Fault Simulation

A study is presented concerning the efficiency of test pattern sets generated with the transition fault model applied to fine grained delay fault models. The authors have developed the delay fault simulator DELFI-a program which is capable of simulating timing failures of combinational circuits using different delay fault models. For the computer experiments the authors selected transition fault test pattern sets because they are very cost-effective to generate. The simulations of benchmark circuits demonstrate that the transition fault test patterns detect gross delay faults even at nodes with redundant stuck-at faults. Furthermore the results show that the transition fault test patterns are not sufficient for small delay faults in the range of a few gate delays. In order to receive a satisfactory coverage for these delay faults, the transition fault test sets must be extended. >

In this paper, we propose a method of diagnosing gate delay faults using delay fault simulation. In the method, suspected faults are deduced by fault simulation and backward path-tracing using diagnostic test-pairs with observed faulty responses. Also, by fault simulation using diagnostic test-pairs with fault-free responses, non-existent faults are deduced, and they are removed from the set of suspected faults. Finally, we present experimental results on the ISCAS'85 benchmark circuits. The experimental results show that by simple processes of backward path-tracing and fault simulation, this method achieves reasonable diagnostic resolutions in a short time.

~ 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.

Increasingly, VLSI systems are being designed using macro blocks and predesigned cores. Since the clock rate at which these circuits operate is steadily increasing, it is important to perform delay testing on modern VLSI chips and systems. Algorithms for delay test generation and delay fault simulation are known to be compute-intensive. Many of these algorithms require gate-level descriptions of circuits which are difficult to generate and may be even impossible to provide when the designer has made use of predesigned cores. Hierarchical testing appears to be an attractive alternative in such cases. Tests generated for logic blocks may be reused to generate tests for larger systems comprising of the logic blocks, hence reducing the total effort in test generation. Tests show in this paper that the computational effort spent in fault simulation can also be reduced using a hierarchical approach. The simulator HIDEFS described in this paper exploits the modular nature of the circuit to save on the memory requirement as well as execution time requirement of fault simulation.

With the increased densities of integrated circuits, several different types of faults can occur. Faults in digital circuits resulting from random defects can introduce DC (stuck-at) faults as well as AC (delay) faults. Previous work in statistical modeling and analysis for delay fault testing generally assumes that at most a single delay fault can occur along any given path in the circuit under test. In this paper we investigate the statistical effect of multiple delay faults along any path in a circuit under test, and predict the path delay fault probabilities as well as the maximum number of path delay faults for both combinational and sequential benchmark circuits. We begin with the development of a statistical model for path delay faults in VLSI circuits [4], which takes into account multiple delay faults along any signal path.

Article Free Access Share on Delay fault coverage and performance tradeoffs Authors: William K. Lam View Profile , Alexander Saldanha View Profile , Robert K. Brayton View Profile , Alberto L. Sangiovanni-Vincentelli View Profile Authors Info & Claims DAC '93: Proceedings of the 30th international Design Automation ConferenceJuly 1993Pages 446–452https://doi.org/10.1145/157485.164970Published:01 July 1993Publication History 89citation253DownloadsMetricsTotal Citations89Total Downloads253Last 12 Months17Last 6 weeks1 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

In the past, research on delay fault testing has been focused on test generation using various delay fault models on full scan gate level netlists. These tests are not very suitable for speed-binning since the confidence that the slowest paths have been covered is low. We have developed a novel methodology with an accompanying tool flow called SpeedGrade that performs path delay fault simulation using an RTL (Register Transfer Level) simulator. This novel method was used to translate the gate level path excitation conditions into higher level of abstraction without loss of accuracy. The higher efficiency of the RTL-based solution allowed for fault grading of functional patterns against the top critical paths in commercial microprocessor designs. The RTL-based approach also had the added benefit of being easier to use for debugging critical paths.

An efficient delay test generation (DTEST GEN) system for combinational logic circuits is presented. In the DTEST GEN system, delay testing problems are divided into gross delay faults and small delay faults separately so that the tradeoff between the levels of delay testing effort and the confidence levels of proper system operation can be explored. Complete automatic test pattern generation (ATPG) algorithms are proposed for both gross delay faults and small delay faults. A novel timing analysis method for delay test generation which uses a conventional depth-first search technique and a novel functionality analysis technique is introduced. The functionality analysis technique examines, necessary conditions for a given delay fault to be testable and estimates the upper bound of the good circuit propagation delay of the longest sensitizable path passing through the fault site. Several benchmark results are demonstrated for both gross delay fault testing and small delay fault testing. >

A prototype version of a new switch-level fault simulator for digital MOS IC's is described. The simulation program, which is called CSASIM, analyzes CSA (connector-switch-attenuator) circuit models using multiple logic values. A novel method of signal evaluation is employed, based on the super-position of bidirectional static and dynamic signals. CSASIM also allows efficient simulation of many different fault types, including stuck-at-constant, open-circuit, short-circuit, and delay faults. The internal structure and fault-simulation mechanisms of the simulator are discussed in this paper.

A prototype version of a new switch-level fault simulator for digital MOS IC's is described. The simulation program, which is called CSASIM, analyzes CSA (connector-switch-attenuator) circuit models using multiple logic values. A novel method of signal evaluation is employed, based on the super-position of bidirectional static and dynamic signals. CSASIM also allows efficient simulation of many different fault types, including stuck-at-constant, open-circuit, short-circuit, and delay faults. The internal structure and fault-simulation mechanisms of the simulator are discussed in this paper.

Testing for delay faults in heavily gated clock designs has the major test challenges of reduced fault coverage and high test power consumption. In the scan-test method, gated clocks are often simplified and replaced with global test clocks. As such, partial clocking by the gated clocks is not inherited in test operations. Global clocking suffers from delay fault coverage loss because a sensitization state cannot easily be created due to the increased state dependence in functional paths, as compared to partial clocking. The global clocking scheme in the test mode is not adequate for low-power designs either, because the power consumed during a test operation exceeds that used during a normal operation. The power grid may not be sufficient to support the power drawn during testing, perhaps resulting in overkilled devices. It is therefore critical that power consumption be maintained under a safe limit, even during testing. In the proposed method, partial clocking in gated designs is preserved to the maximum possible to create more reachable states, thereby increasing transition fault coverage and reducing test power during launch and capture cycles. A transition fault simulator was developed, and it demonstrated higher transition fault coverage and reduced test power for ISCAS-89 circuits when partial clocking is used.

Evaluation of delay fault testability of LUTs for the enhancement of application-dependent testing of FPGAs

An approach to generate test pattern for the path delay fault model using a modified stuck-at TPG tool which has been used for industrial purposes for years is presented. We discuss constraints derived by the definition of non-robust delay tests and show that, under some circumstances, the requirements accepted in literature are not sufficient to derive non-robust tests due to possible test invalidation, even in the absence of any additional faulty delay. Finally, we discuss possible constraints which have influence on the test quality and show that test generation for robust tests can not be tackled if a stuck-at TPG tool is used without any delay fault simulation.

Test generation and fault simulation of path delay faults are very time-consuming. A new fault simulation method of fully enhanced scan designed circuits is proposed for path delay faults based on single stuck-at tests without circuit transformation. The proposed method identifies robustly and non-robustly testable paths first, for which a selected path circuit (SPC) is constructed. The SPC circuit contains no internal fanouts. Fault simulation of non-robustly testable paths is reduced to 3-valued logic simulation of the SPC circuit. Fault simulation is completed on the SPC circuit by only tracing the active part of SPC circuit. An effective fault dropping technique is also adopted based on the selective tracing scheme. The proposed fault simulation scheme is extended to that of robustly testable path delay faults. Experimental results confirm that the proposed fault simulator is exact. It is shown according to experimental results that the proposed fault simulator gets exact fault simulation results in very short time. Sufficient experimental results are presented to compare with previous methods on CPU time and accuracy.

Test generation procedures target a variety of fault models in order to produce test sets that are effective for defect detection. This paper considers the likely scenario where two-cycle skewed-load tests are generated to detect single transition faults, and the test set is complemented with tests for single stuck-at faults that are not detected by the transition fault test set. For this scenario, this paper makes several unique observations that can be utilized to produce a single compact test set that consists only of two-cycle skewed-load tests for both fault models. The first observation is that a single-cycle test for a stuck-at fault can be transformed into a skewed-load test that is guaranteed to detect the stuck-at fault without performing logic or fault simulation. The second observation is that skewed-load tests, which are transformed from single-cycle tests for stuck-at faults, sometimes detect more transition and stuck-at faults than tests that were generated for transition faults. The third observation is that a static test compaction procedure, which is based on the modification and removal of tests, is effective in this context because it allows tests for stuck-at faults to detect more transition faults and vice versa. This paper describes a test compaction procedure based on these observations and presents experimental results for benchmark circuits to demonstrate the effectiveness of the procedure.