Linear Time Compactor X-Masking Reduction via Segmented Scan Chains
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Solution Overview
Problem
Linear time compactors face challenges in reducing the X-masking effect, which occurs when unknown states (X-values) in test response data lead to reduced observability and increased error masking, especially with high compression ratios, requiring improved methods to minimize X-masking and enhance test data compression efficiency.
Innovation Solution
The proposed solution involves an augmented test architecture with a dual-segment register configuration, including multiple-input shift-registers and single-input shift-registers, which generates and combines compressed test response bits in a way that minimizes X-masking by dividing scan chains and shift cycles into mutually exclusive groups, ensuring unique erroneous signatures and efficient unloading of compacted test response vectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high compression ratio is used in linear time compactor, then test data compression efficiency is improved, but X-masking effect increases and observability deteriorates
Solution Approach 1:
The compactor is divided into multiple segments, each handling a subset of scan chains. This segmentation allows the system to maintain high compression ratios while reducing the density of X-values in each segment's output, thereby preserving observability. Each segment processes a manageable portion of the test response data, preventing X-masking from becoming overwhelming.
Solution Approach 2:
Multiple intermediate compacted test response vectors are generated before final combination. These intermediate vectors act as mediators that distribute and manage X-values across different processing paths. By introducing these intermediate stages, the system can achieve high overall compression while maintaining lower local X-density, thus reducing X-masking effects.
2Quantity of substance
If linear time compactor is used to compact test response data, then test data volume is reduced, but X-masking and error masking increase
Solution Approach 1:
The compaction process is segmented into multiple stages, each producing a compacted test response vector. By dividing the overall compaction into segments, the system achieves significant data volume reduction while ensuring that each segment's contribution to X-masking is limited and manageable, preventing cumulative masking effects.
Solution Approach 2:
The system changes parameters such as the number of segments, the distribution of scan chains across segments, and the combination strategy of intermediate vectors. These parameter adjustments optimize the balance between data compression ratio and X-masking reduction, allowing effective compaction while minimizing harmful masking effects.
3Device complexity
If scan chains are grouped into fewer groups, then device complexity is reduced, but X-masking effect increases due to higher density of X-values
Solution Approach 1:
Scan chains are divided into multiple groups, each processed by a separate segment of the compactor. This segmentation increases the number of groups but distributes X-values more evenly across segments, reducing the local density of X-values in each group's output and thereby decreasing X-masking effects.
Solution Approach 2:
The system transitions from a single-dimension compaction approach to a multi-dimensional approach by organizing scan chains into groups across multiple segments. This dimensional change allows the system to manage X-value distribution more effectively, reducing X-masking while the overall structure remains organized and manageable.
Data Source
AI summary
A proposed linear time compactor (LTC) with a means of significantly reducing the X-masking effect for designs with X's and supports high levels of test data compression where:1) The LTC consists of two parts that are unloaded into a tester through an output serializer.2) The first part is unloaded per t shift cycles while the second part is unloaded once per test pattern.3) One part of the LTC divides scan chains into groups such that X-masking effect between groups of scan chains is impossible.4) One part of LTC divides shift cycles into groups such that X-masking effect between groups of shift cycles is impossible.Consequently, the X-masking effect in the proposed LTC is significantly reduced.