Unknown Blocking Scheme for Low Control Data Volume and High Observability

Abstract

This paper presents a new blocking logic to block unknowns for temporal compactors. The proposed blocking logic can reduce data volume required to control the blocking logic and also increase the number of scan cells that are observed by the temporal compactors. Control patterns, which describe values required at the control signals of the blocking logic, are compressed by LFSR reseeding. In this paper, the blocking logic gates for some groups of scan chains that do not capture unknowns are bypassed. Since all the scan cells in these scan chain groups are observed without specifying the corresponding bits in control patterns, fewer specified bits are required and more scan cells are observed. The seed size is further reduced by reducing numbers of specified bits in the densely specified control patterns. The proposed method can always achieve the same fault coverage that can be achieved by direct observation of scan chains. Experiments with large industrial designs clearly demonstrate that the proposed method is scalable to large circuits. Hardware overhead for the proposed blocking logic is very low.

Optimal unknown bit filtering for test response masking

“…Typically, [12] a set of test patterns that is generated by an ATPG to achieve high fault coverage detects most faults multiple times. In other words, most faults are detected by more than one test pattern in the set, this kind fault call multiple detection fault, otherwise, a fault detect in only one test pattern in the set is call single detection fault.…”

“…The X-block method [11] uses the same technique but requires less control data and simpler test logic. The unknown blocking scheme of [12] deploys the LFSR reseeding as well. [13] the masking signals are formed by AND-ing several outputs of a phase shifter to decrease probability of blocking non-X responses.…”

Constructing Augmented Multimode Compactors

“…Significant improvement in the X-tolerant capabilities of the compactors was achieved based on masking and selection using control per test, control per shift or combined control [13][14][15][16][17][18][19]. Most of the presented schemes are compatible with certain types of decompressors and compressors.…”

Highly X-Tolerant Selective Compaction of Test Responses

“…The X-block method [21] uses the same technique but requires less control data and simpler test logic. The unknown blocking scheme of [22] deploys the LFSR reseeding as well. However, it takes advantage of the fact that the majority of scan chains do not capture X states to reduce the amount of control data.…”