Scan Chain Reconfiguration for Test Time Reduction
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Solution Overview
Problem
Conventional scan compression architectures face challenges in efficiently testing integrated circuits due to clustering of care bits within a few flip-flops, which complicates the mathematical equations solved by the decompression circuit, leading to inefficient test patterns and potential fault dropouts.
Innovation Solution
The proposed solution involves segmenting scan chains into multiple segments, adding multiplexers at the endpoints, and rearranging the segments based on a select signal to spread care bits across the time domain, thereby improving the controllability and observability of the test patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If scan chains are tested using conventional compression architectures, then test data volume is reduced, but care bits cluster within a few flip-flops complicating the mathematical equations
Solution Approach 1:
The scan chain is divided into multiple segments with multiplexers inserted at segment boundaries. This segmentation allows care bits to be distributed across different segments rather than clustering in a few flip-flops, simplifying the mathematical equations solved by the decompression circuit while maintaining test data volume reduction.
2Reliability
If care bits are clustered in conventional architectures, then decompression circuit equation solving becomes complex, but test coverage is compromised due to fault dropouts
Solution Approach 1:
By segmenting the scan chain and inserting multiplexers at segment boundaries, care bits are distributed across segments. This reduces decompression circuit complexity and prevents fault dropouts, thereby improving test coverage and reliability.
Solution Approach 2:
The multiplexers enable dynamic reconfiguration of scan chain segments, allowing flexible distribution of care bits across different segments. This dynamic capability simplifies the mathematical equations while maintaining comprehensive fault detection coverage.
3Productivity
If test patterns are generated for clustered care bits, then test generation is simplified, but test time increases due to inefficient patterns
Solution Approach 1:
Segmenting the scan chain distributes care bits across multiple segments, enabling more efficient test patterns that reduce the number of cycles required to detect faults, thereby decreasing overall test time while maintaining pattern generation simplicity.
Solution Approach 2:
The dynamic reconfiguration capability allows test patterns to be optimized for different segment configurations, improving pattern efficiency and reducing test time without complicating the test generation process.
4Reliability
If additional compression engines are used to improve test coverage, then fault detection capability increases, but device complexity and cost increase
Solution Approach 1:
Instead of adding more compression engines, the scan chain is segmented with multiplexers that distribute care bits across segments. This approach improves fault detection capability for hard-to-detect faults without increasing device complexity or requiring additional compression engines.
Data Source
AI summary
According to an embodiment, a first aspect relates to a method for testing a scan chain. The method includes segmenting the scan chain into two or more segments; adding a respective multiplexer at end points of each segment, wherein each pair of sequential segment shares a common multiplexer in between; asserting a select signal at a select terminal of the multiplexers such that a relative position of the two or more segments is rearranged positionally in a rearranged scan chain; generating a test pattern to be communicated to an input terminal of the rearranged scan chain and observing a test result at an output of the rearranged scan chain; and determining a fault condition in the rearranged scan chain based on comparing the test result and an expected result.