Broadside Test Set Research Articles

Covering Test Holes of Functional Broadside Tests

Functional broadside tests were developed to avoid overtesting of delay faults. The tests achieve this goal by creating functional operation conditions during their functional capture cycles. To increase the achievable fault coverage, close-to-functional scan-based tests are allowed to deviate from functional operation conditions. This article suggests that a more comprehensive functional broadside test set can be obtained by replacing target faults that cannot be detected with faults that have similar (but not identical) detection conditions. A more comprehensive functional broadside test set has the advantage that it still maintains functional operation conditions. It covers the test holes created when target faults cannot be detected by detecting similar faults. The article considers the case where the target faults are transition faults. When a standard transition fault, with an extra delay of a single clock cycle, cannot be detected, an unspecified transition fault is used instead. An unspecified transition fault captures the behaviors of transition faults with different extra delays. When this fault cannot be detected, a stuck-at fault is used instead. A stuck-at fault has some of the detection conditions of a transition fault. Multicycle functional broadside tests are used to allow unspecified transition faults to be detected. As a by-product, test compaction also occurs. The structure of the test generation procedure accommodates the complexity of producing functional broadside tests by considering the target as well as replacement faults together. Experimental results for benchmark circuits demonstrate the fault coverage improvements achieved, and the effect on the number of tests.

Functional Broadside Tests Under Broadcast Scan

Under broadcast scan, scan chains are partitioned into groups that receive the same scan-in values. This article considers, for the first time, the application of functional broadside tests under broadcast scan. This article provides a definition of a close-to-functional broadside test that is applicable under a broadcast scan configuration. The test is referred to as a group-functional broadside test. This article describes how a subset of group-functional broadside tests is obtained from a functional broadside test and discusses the proximity to functional operation conditions that a group-functional broadside test maintains. It also describes the generation of a group-functional broadside test set. The experimental results for transition faults in benchmark circuits explore the tradeoff between the level of test data compression, the proximity to functional operation conditions, and the transition fault coverage, by considering scan configurations with different numbers of scan chains.

Broadside Tests for Transition and Stuck-At Faults

A recent work showed that it is possible to transform a single-cycle test for stuck-at faults into a skewed-load test that detects the same stuck-at faults without performing logic or fault simulation. By using this transformation, it is possible to generate a compact skewed-load test set for stuck-at and transition faults. The advantage for test compaction is related to the fact that the test set contains a single test type. For cases where broadside tests are preferred over skewed-load tests, this article studies the possibility of transforming a single-cycle test into a broadside test, and generating a compact broadside test set for stuck-at and transition faults. This article addresses several challenges in order to achieve this goal without resorting to sequential test generation or state justification that have a high computational complexity. The experimental results for benchmark circuits demonstrate the levels of test compaction that can be achieved using small numbers of observation points.

Extracting a Close-to-Minimum Multicycle Functional Broadside Test Set From a Functional Test Sequence

Functional broadside tests avoid overtesting of delay faults that may occur with scan tests. Functional broadside tests can be extracted from a functional test sequence. This paper describes a procedure for extracting a close-to-minimum set of multicycle functional broadside tests from a functional test sequence. The procedure uses a modified sequential fault simulation process to collect information about detectable faults. This process indicates which faults must be detected by scan-out operations of multicycle tests, and which ones can be detected on primary outputs. The procedure uses a set-covering procedure to select a close-to-minimum set of clock cycles for scan-out operations. Every scan-out operation is complemented into a multicycle test. In addition, the procedure selects at most one test for faults that can be detected on the primary outputs. Experimental results are presented for benchmark circuits to demonstrate various features and extensions of the procedure.

Switching Activity of Faulty Circuits in Presence of Multiple Transition Faults

Excessive switching activity in the fault-free circuit can cause a fault-free circuit to fail because of increased delays. For the same reason, excessive switching activity in a faulty circuit can cause a delay fault to escape detection. This paper observes that the switching activity is higher in the presence of multiple delay faults with higher multiplicities (larger numbers of single faults that are present in the circuit together). The challenge in addressing multiple faults is related to their large number. This paper addresses this challenge by an iterative procedure that is applied to transition faults under a low-power broadside test set, and has two subprocedures: 1) the first subprocedure finds multiple transition faults with excessive faulty switching activity and 2) the second subprocedure modifies the test set so as to avoid excessive faulty switching activity for the faults found by the first subprocedure. With every additional iteration there are fewer multiple transition faults that exhibit excessive faulty switching activity. The experimental results for benchmark circuits demonstrate the levels of excessive faulty switching activity in the presence of multiple transition faults, and the possibility of reducing or even eliminating it after a small number of iterations.

Reverse Low-Power Broadside Tests

This paper defines a new type of a low-power broadside test, called a reverse low-power broadside test, whose application requires design-for-testability logic. The unique feature of a reverse low-power broadside test is that it duplicates the switching activity during the second functional capture cycle of a given low-power broadside test, except that signal-transitions are reversed. Thus, the switching activity of a reverse low-power broadside test duplicates that of a low-power broadside test in every subcircuit and on every line individually. In addition, the reversed test detects different faults, and can thus increase the fault coverage of a low-power broadside test set. This paper studies the ability of reverse low-power broadside tests to increase the transition fault coverage in benchmark circuits considering functional broadside tests as well as low-power broadside tests that are not functional.

Enhanced Test Compaction for Multicycle Broadside Tests by Using State Complementation

Multicycle tests support test compaction by allowing each test to detect more target faults. The ability of multicycle broadside tests to provide test compaction depends on the ability of primary input sequences to take the circuit between pairs of states that are useful for detecting target faults. This ability can be enhanced by adding design-for-testability (DFT) logic that allows states to be complemented. This article describes a test compaction procedure that uses such DFT logic to form a compact multicycle broadside test set for transition faults where the tests use constant primary input vectors. The use of complemented states also allows the procedure to increase the transition fault coverage beyond the transition fault coverage of a broadside test set. The procedure has the option of increasing the switching activity of the tests gradually in order to explore the tradeoff between the number of tests, the fault coverage, and the switching activity.

Piecewise-Functional Broadside Tests Based on Reachable States

This paper describes a new characterization of broadside tests that measures the proximity to functional operation conditions during their functional clock cycles, where delay faults are detected. Proximity to functional operation conditions is important for avoiding overtesting of delay faults. The new characterization considers a test as piecewise-functional based on its scan-in state. For functional operation conditions, the scan-in state must be a reachable state (a state that the circuit can enter during functional operation). However, using only reachable states as scan-in states limits the fault coverage that can be achieved. In a piecewise-functional broadside test, the scan-in state can be partitioned into substates that are also substates of reachable states. The paper presents a definition that allows every broadside test to be characterized as piecewise-functional. It also describes procedures for characterization, and for modification of broadside test sets so as to ensure that they create closer-to-functional operation conditions.

Skewed-Load Test Cubes Based on Functional Broadside Tests for a Low-Power Test Set

A low-power test generation procedure that was developed earlier merges broadside test cubes that are derived from functional broadside tests in order to generate a low-power broadside test set. This has several advantages, most importantly, that test cubes, which are derived from functional broadside tests, create functional operation conditions in subcircuits around the sites of detected faults. These conditions are preserved when a test cube is merged with other test cubes. This brief applies a similar approach to the generation of a low-power skewed-load test set. The main challenge that this paper addresses is the derivation of skewed-load test cubes from functional broadside tests. The paper also considers the percentages of values that should be unspecified in the skewed-load test cubes in order to balance the need to create functional operation conditions with the need for test compaction.

Design-for-testability for multi-cycle broadside tests by holding of state variables

This article describes a design-for-testability approach for increasing the transition fault coverage of multi-cycle broadside tests. Earlier methods addressed two-cycle tests. The importance of multi-cycle tests results from the ability to produce more compact test sets than possible with two-cycle tests, from the fact that when multi-cycle tests are applied at-speed, they can detect defects that are not detected by two-cycle tests and from their ability to avoid overtesting of delay faults. The approach described in this article is based on holding the values of selected state variables constant during the functional clock cycles of a multi-cycle broadside test. This allows new tests to be produced, which are different from broadside tests, without relying on nonfunctional toggling of state variables as in earlier methods for two-cycle tests. Experimental results show significant improvements in transition fault coverage using a fixed set of hold configurations for two types of multi-cycle broadside test sets: (1) test sets that are stored and applied from an external tester, and (2) functional broadside test sets that are generated using on-chip hardware.

Low-power skewed-load tests based on functional broadside tests

This article studies the generation of low-power skewed-load tests such that the signal transitions (and line values) they create during their fast functional clock cycles match those of functional broadside tests. Functional broadside tests create functional operation conditions during their fast functional clock cycles. As a result, the signal transitions that occur during these clock cycles can also occur during functional operation. The procedure described in this article matches these signal-transitions on a line-by-line basis when generating low-power skewed-load tests. The procedure accepts a functional broadside test set for transition faults. In one of its basic steps, the procedure modifies a functional broadside test into a skewed-load test. This allows it to retain many of the signal transitions (and line values) of the functional broadside test in the skewed-load test. Experimental results for benchmark circuits demonstrate the extent to which it is possible to match the signal-transitions of skewed-load tests with those of functional broadside tests while achieving the high transition fault coverage that is typical of skewed-load tests.

Transition Fault Simulation Considering Broadside Tests as Partially-Functional Broadside Tests

The scan-in states of functional broadside tests are reachable states, which are states that the circuit can enter during functional operation. This is used for ensuring functional operation conditions during the functional clock cycles of the tests. For a partially-functional broadside test, the scan-in state has a known Hamming distance to a reachable state. This ensures measurable deviations from functional operation conditions during the functional clock cycles of the test. It is important for addressing overtesting as well as excessive power dissipation. This brief develops a fault-simulation procedure for transition faults under arbitrary (functional and nonfunctional) broadside tests that considers the tests as partially-functional broadside tests. The procedure can be used for evaluating the proximity to functional operation conditions of arbitrary broadside test sets. For illustration, the procedure is used for comparing a low-power test set with an arbitrary broadside test set.

On the Computation of Common Test Data for Broadside and Skewed-Load Tests

Skewed-load and broadside tests complement each other and allow higher delay fault coverage to be achieved for a standard-scan circuit that supports both types of tests. The difference between the two types of tests is mainly in the test application process. The input test data required for both of them are similar. This similarity is used in this work to compute compact input test data that can be used as a basis for forming both types of tests. It results in improved fault coverage compared to the use of broadside (or skewed-load) tests alone, and in reduced test data volume compared to the case where broadside and skewed-load tests are stored separately. Experimental results are presented using a procedure that accepts a test set of any type, and computes input test data suitable for the application of both types of tests. The procedure modifies the test data so as to compact it as well as increase the fault coverage. The procedure is applied to a broadside test set and to mixed test sets that consist of both types of tests.

Generation of Multi-Cycle Broadside Tests

The use of multi-cycle (or multi-pattern) tests for delay faults can reduce the number of clock cycles required for test application, and enhance the ability of a test set to detect delay defects. This is achieved by exercising the circuit in functional mode for several clock cycles as part of each test. This advantage is especially important for multi-pattern functional broadside tests, which guarantee normal functional operation conditions during the functional clock cycles of the test. This paper describes a procedure for generating multi-pattern broadside tests. The procedure extends a two-pattern test set gradually to increase the number of patterns included in each test while reducing the number of tests. Experimental results demonstrate that significant reductions in the numbers of clock cycles are possible with the proposed procedure for both functional and arbitrary broadside test sets.

Functional Broadside Tests with Minimum and Maximum Switching Activity

Functional broadside tests were defined as broadside tests that detect target faults using only states that the circuit can visit during functional operation. With functional broadside tests, the peak switching activity and current demands during fast capture cycles can be guaranteed not to exceed those of functional operation, avoiding overtesting due to current demands that cannot be met. Therefore, functional broadside tests make it possible to explore tests with different switching activities as a way to maximize defect detection. For example, a test with a higher switching activity exercises more circuit lines, and is thus likely to activate and detect more defects. In addition, the maximum switching activity under functional broadside tests can be used as an upper bound on the switching activity that can be allowed for other types of tests. Tests with low switching activity may be preferred during wafer testing. Motivated by these applications, we study the range of switching activity possible for the functional broadside tests that detect a target fault, considering transition faults. We use the results to evaluate (low-power) standard broadside test sets.

Scan-Based Delay Test Types and Their Effect on Power Dissipation During Test

The peak power dissipated in nonscan logic during fast capture cycles of scan-based two-pattern tests for path delay faults is considered. It is first demonstrated that the peak-power dissipation for an enhanced-scan test set, which has the smallest peak-power dissipation, is lower than that for a skewed-load test set and that the peak-power dissipation for a skewed-load test set, which has the smallest peak-power dissipation, is typically (but not always) lower than that for a broadside test set. Test sets that consist of more than one type of tests are then considered. Skewed-load and broadside tests may be used together to improve the fault coverage when this is permissible by a standard scan design. It is demonstrated that using both types of tests can sometimes reduce the peak-power dissipation. Results are also presented of an experiment where an arbitrary test set of one type is modified to reduce the peak power without reducing the fault coverage by introducing tests of another type.

Generation of Functional Broadside Tests for Transition Faults

Scan design allows a circuit to be tested using states that the circuit cannot enter during functional operation. It was observed that nonfunctional operation during testing may cause excessive currents that can cause a good chip to fail the test because of voltage droops caused by the excessive current demand. A good chip may also fail due to the propagation of signal transitions along nonfunctional long paths, especially during at-speed testing. This problem is studied in this paper in the context of tests for transition faults. A method for determining transition faults that are untestable under functional operation-conditions is described. Two procedures for generating transition-fault tests that use only functional operation conditions are also described. The first procedure accepts as input a broadside test set for transition faults. The second procedure accepts as input a test sequence for the nonscan circuit. Although such a test sequence is more complex to generate and simulate, it results in higher numbers of faults detected under functional operation conditions