Change output if the preceding count bits are 1 q1 changes whenever q0 1 q2 changes whenever q1q0 11. Pdf on potential fault detection in sequential circuits. Avoid to use latches as possible in synchronous sequential circuits to avoid design problems 58 sr latch. This paper employs the survey on the fault diagnosis methods in binary digital circuits which can be further optimized for ternary digital circuits. Multiple transient faults in combinational and sequential. In this article a method is presented for evaluating the probability of detecting pd a single stuck fault in a sequential circuit as a function of the number of random input test vectors. For the design of sequential error detection circuits very few methods adapted to specific fault models are known. Turn the circuit into a sequential one need a sequence of at least 2 tests to detect a single fault unique to cmos circuits stuckon a single transistor is permanently shorted irrespective of its gate voltage detection of a stuckopen fault requires two vectors detection of a stuckon fault requires the.
Fault modeling of combinational and sequential circuits at. Introduction test generation problem for sequential circuits is intractable. A procedure for detection of faults in a simple controllable linear sequential circuit lsc over gf2 is developed. To detect a fault, a sequence of vectors may be needed. Fault detection methods in sequential systems sciencedirect. Long test sequences a test for a fault in a sequential circuit essentially consists of three parts. Universal length 4 sequence detector this one detects 1011 or 0101 or 0001 or 0111 sequence transformation serial binary adder arbitrary length operands 0 1 000 011 101 010 100 111 110 001 elec 326 8 sequential circuit design 2.
Black box delay fault models for nonscan sequential circuits. The use of threevalue logic for fault simulation of synchronous sequential circuits may incur a loss of accuracy that would cause the fault coverage to be underestimated. Synchronous sequential circuit a path an illustrative network for enf. Pdf fault modeling of combinational and sequential circuits at. Electric fault location data processing, digital integrated circuits testing, sequential machine theory publisher edmonton. Formal sequential circuit synthesis summary of design steps. As the complexity of very large scale integration vlsi is growing, testing becomes tedious and tougher. A fanoutfree combinational circuit with n primary t an input sequence. In this paper we presented a new approach to design faulttolerant combinational circuits.
Therefore, the scan register is additionally introduced into the circuits, which significantly facilitates the. A method is developed for obtaining a highly compressed fault table for twolevel combinational circuits. Fault detection in linear sequential cirucits by aleksa petrovic this thesis is concerned with the detection of non transient faults in digital networks. Assume a logic circuit with minput and noutput lines. Fault diagnosis in sequential circuits sciencedirect. Gatelevel test generation for sequential circuits people. Seth university of nebraska lincoln, nebraska 68588 vishwani d. Later, we will study circuits having a stored internal state, i. Not practical for use in synchronous sequential circuits. The method is based on automatically designing a circuit which.
Hyperactive fault fault induces much internal signal activity without reaching po. For combinational circuits, the limit of this research, the results in all cases were favorable to the test sequence. Initialization fault fault prevents initialization of the faulty circuit. Pdf a fault detection method for combinational circuits. This paper is concerned with the diagnosis of faults in synchronous sequential machines. Estimating the quality of manufactured digital sequential. Asm chart, timing considerations, control implementation design with multiplexers, pla controlasynchronous sequential circuits. But sequential circuit has memory so output can vary based on input. Since there are two types of faults which are, easy to test faults and second one difficult to test faults. The influence of sequential computing on testing can be profound. Design of synchronous counters, shift registers and their e applications. A nonenumerative path delay fault simulator for sequential circuits. Input sequence to set z to 0 in the faultfree circuit.
Flip flop is a sequential circuit which generally samples its inputs and changes its outputs only. As different fault sizes may result in different faulty circuit behaviors, to deal. As of now fault models are used to test digital circuits at the gate level or below that level. A thesis in electrical engineering submitted to the graduate faculty of texas tech university in partial fulfillment of the requirements for the degree of master of science in electrical engineering approved c accepted may, 1975. Reduction of fault latency in sequential circuits by using. Here we use masking of selected positions of test responses in which the value of the fault free response is known in order to avoid detection of faults which should not be detected. Difference between combinational and sequential circuits in combinational circuits, the outputs are at any instant determined only by the present combination of inputs but in sequential circuits, outputs depend on the present input and also on the states of the memory location and elements. Sequential circuits applicable for detecting different types of faults1. Testing 2 fault model stuckat model assume selected wires gate input or output are stuck at logic value 0 or 1 models curtain kinds of fabrication flaws that short circuit.
Analysis j 14j given the logical diagram of a sequential system, it is necessary to observe a minimum of module outputs in order to be capable of understanding its evolution. On redundancy and fault detection in sequential circuits. Testing of logic circuits university of california, berkeley. Faults are defined and classified, the problems of detection and diagnosis are discussed, and a previously presented algorithm for fault detection is outlined. Fault detection in logical circuits by samprakash majumdar, b. Detection of a fault in a sequential circuit requires a sequence of test vectors. This type of circuits uses previous input, output, clock and a memory element. This method obtains testing sequences by forcing the.
In this course material we design and analyze only synchronous sequential logic. Reduction of fault latency in sequential circuits by using decomposition ilya levin i. A circuit with two crosscoupled nor gates or two crosscoupled nand gates. A signal can assume different values in the faultfree and faulty circuits. The circuit is partitioned into three parts, the input and output combinational logic and the memory. That is the new faulty circuit and the fault free circuit is simulated and. For sequentially untestable faults, chengbadopted an approach defining a feedback free circuit model in which he cut several feedback lines from the original circuit to obtain a combina tional model. Hughes, virgil willis, fault diagnosis of sequential circuits 1969. Pdf on redundancy and fault detection in sequential circuits. Consequently the output is solely a function of the current inputs. Combinational test to activate the fault, and bring its effect to the boundary of the combinational logic. He found socalled feed back free sequential redundancies from the combinational model using a test generator. Pdf fault detection and test minimization methods for. Asynchronous asynchronous sequential circuits internal states can change at any.
Optimal error detection circuits for sequential circuits. Testing of logic circuits fault models test generation and coverage fault detection design for test cs 150 fall 2005 lec. There have been just a few approaches that tackle this issue 11120, however, only the work we proposed in 20 models transient faults in sequential circuits, while also including all the other important modeling aspects listed above. A discrete parameter markovmodel is used in the analysis to obtain closedform expressions for pd. A set of operations is defined through which the minimal test set for detecting stuckat faults is obtained from the compressed fault table. Pdf on redundancy and fault detection in sequential. We must develop efficient fault detection and location methods in order.
Testing of sequential circuits wit solapur professional learning community. Fault modeling of combinational and sequential circuits at register transfer level. If the fault is in the memory elements, observation of the faulty state in one of the primary outputs. Basic concept of fault detection and location in sequential circuits notes edurev notes for is made by best teachers who have written some of the best books of.
To ensure that only fault free systems are delivered. The faultdetection test set for a combinational circuit using the pathsensitizing method is very attractive from the point of two basic approaches. This article describes an emulationbased method for locating stuckat faults in combinational and synchronous sequential circuits. Input signals change one at a time and only when the circuit is in the stable state. The probability of error detection in sequential circuits. In this method, we use hardware redundancy to add a redundant output signal to the circuit. First approach is to examine each view of not requiring the construction of the fault table and is individual fault. Sequential circuit design university of pittsburgh.
Difference between combinational and sequential circuits. Synchronous asynchronous primary difference 94 synchronous vs. Identifying untestable faults in sequential circuits i. A gatedelay fault simulator for sequential circuits. On application of output masking to undetectable faults in.
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