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Recent studies have shown that new tests are required for the detection of a large percentage of scan cell internal open faults which are not detected by the existing tests. However, the additional coverage due to the new tests drops significantly when opens with moderate resistances are considered. In this paper we propose to augment earlier test methods to detect internal scan chain opens with a...
In many designs asynchronous inputs are used to set and/or reset flip-flops. Considering a scan cell implementation used in an industrial design we show that stuck-open faults in some transistors driven by asynchronous inputs require two new flush tests. Such faults, if left undetected, cause functional failures. The two new tests increase the overall stuck-open fault coverage of each scan cell by...
The objective of using logic BIST for online and periodic testing is to identify defects, like opens, resulting from the wear and tear of the circuit. We have shown that existing test sets have a low coverage for open defects located in scan flip-flops, even though such defects may affect functional operation. Existing Logic BIST structures suffer from the same limitations. A novel Logic BIST architecture...
We describe a synthesis-for-testability approach targeting broadside testing of transition faults. We refer to this process as synthesis for broadside testability. Unlike design-for-testability (DFT) procedures that require additional control inputs to implement DFT modes of operation, synthesis for broadside testability uses only the standard scan design and relies on broadside tests to detect target...
Scan chains contain approximately 50% of the logic transistors in large industrial designs. Yet, faults in the scan cells are not directly targeted by scan tests and assumed detected by flush tests. Reported results of targeting the scan cell internal faults using checking sequences show such tests to be about 4.5 times longer than scan stuck-at test sets and require a sequential test generator, even...
The use of multiple scan chains was shown to improve the coverage of transition faults achieved by skewed-load tests. For broadside tests, the number of scan chains does not affect the transition fault coverage. We describe an enhanced broadside configuration under which increasing the number of scan chains helps increase the fault coverage. In the enhanced configuration, the first flip-flop of a...
Autoscan is a design-for-testability approach proposed earlier that uses scan chains without external scan inputs or outputs in order to reduce the test application time and test data volume of scan. We describe three improvements to the basic autoscan design-for-testability approach based on the following observation. Under autoscan, due to the elimination of external scan inputs, the first flip-flop...
We propose a design-for-testability technique for synchronous sequential circuits called autoscan. Autoscan uses scan chains similar to conventional scan. However, it gives up the external scan inputs and outputs in order to eliminate the test data volume associated with them. Scan operations under autoscan improve the circuit testability by allowing the circuit state to be modified through shifting...
Testing of delay faults require two pattern tests. Broadside and skewed-load testing are two approaches to test for delay faults in scan designs. The broadside approach is often preferred over the skewed-load approach in designs that also use the system clock for scan operations, since skewed-load requires a fast (at-speed) scan enable signal while broadside testing does not. In this paper, we propose...
We describe a novel method to partition flip-flops in scan chains into disjoint groups of flip-flops that are to be driven by independent scan enable signals to achieve higher delay fault coverage. The proposed method to partition flip-flops is motivated by our recent work which demonstrated that driving subsets of flip-flops by independent scan enable signals to launch signal transitions will lead...
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