Partial-scan built-in self-testing circuit having improved testability
First Claim
1. A digital circuit having an improved ability to be electronically tested by test signals applied thereto comprising:
- a sequential network having a near-acyclic structure, the network having at least one node therein at which a fault may occur;
a test pattern generator coupled to the network for supplying successive test patterns thereto to cause the network to generate a response following receipt of each successive pattern;
an electronic logic block coupled to the network for compacting the response generated thereby; and
the digital circuit being characterized by at least one test point added within the sequential network to improve the testability thereof, the test point being added at a node selected such that the node has a separate one of its controllability and observability probabilities different from a prescribed value therefor and a detection probability below a prescribed value therefor prior to the addition of the test point, and insertion of the mode increases fault coverage during testing.
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Accused Products
Abstract
The testability of a near-acyclic circuit (14) can be enhanced by the addition of one or more control points (36) and observation points (34) to allow for increased observability and controllability of selected nodes (28). The control points (36) and/or test points (34) are added by first computing the controllability, observability and fault detection probability at each node. A fault is then selected. If either the controllability or observability for such fault is not inside a prescribed value range, and the fault detection probability is below a prescribed value, then either a control point (36) and/or a observation point (34) may be added.
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Citations
14 Claims
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1. A digital circuit having an improved ability to be electronically tested by test signals applied thereto comprising:
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a sequential network having a near-acyclic structure, the network having at least one node therein at which a fault may occur; a test pattern generator coupled to the network for supplying successive test patterns thereto to cause the network to generate a response following receipt of each successive pattern; an electronic logic block coupled to the network for compacting the response generated thereby; and the digital circuit being characterized by at least one test point added within the sequential network to improve the testability thereof, the test point being added at a node selected such that the node has a separate one of its controllability and observability probabilities different from a prescribed value therefor and a detection probability below a prescribed value therefor prior to the addition of the test point, and insertion of the mode increases fault coverage during testing. - View Dependent Claims (2, 3, 4, 5)
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6. A method for modifying a near-acyclic circuit to improve its testability by adding at least one test point thereto to increase the level of fault coverage when the circuit is tested by applying a successive one of t random test patterns thereto, comprising the steps of:
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(a) computing the controllability, observability and detection probabilities of each node in the circuit; (b) selecting a fault for a given one of the nodes; (c) adding a test point at a particular node when a separate one of the controllability and observability probabilities for the node is not within a prescribed value range for each value therefor and the detection probability is below a prescribed value therefor; and (d) repeating the steps of (a)-(c) until either the fault coverage no longer increases or until no more faults can be selected. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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7. The method according to 6 wherein the test point which is added comprises an observation point.
Specification