Selective Reseeding for Scan Test Compression
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Solution Overview
Problem
Current scan testing methods for integrated circuits (ICs) face inefficiencies due to high test data volume and application time, especially with increasing complexity and shrinking process technologies, leading to insufficient cost control and reduced fault coverage.
Innovation Solution
A scan test system utilizing a dual-PRPG architecture with compressor and decompressor structures (CODECs) and an instruction decode unit (IDU) for selective reseeding, which enables efficient data compression and decompression, reducing test pattern volume and application time while maintaining high fault coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deterministic ATPG is used to generate test patterns, then fault coverage is improved, but storage area in tester and test application time increase significantly
Solution Approach 1:
The patent divides the large set of deterministic ATPG test patterns into multiple smaller subsequences, each generated by a separate PRPG instance. This segmentation allows the tester to store and apply much smaller data sets while maintaining comprehensive fault coverage through coordinated operation of multiple PRPGs.
Solution Approach 2:
The patent introduces on-chip compression structures (scan compressors and response compressors) as intermediaries between the tester and the DUT. These structures compress the test data before it enters the scan chains and compress the test responses before they leave the DUT, significantly reducing the data volume that must be stored and transferred by the tester.
2Quantity of substance
If on-chip compression structures are added to reduce test data volume, then tester storage requirements are reduced, but device complexity increases
Solution Approach 1:
The patent designs the on-chip compression structures to serve multiple functions: scan chain loading, test pattern generation, and test response collection. The same PRPG instances and compression structures are used for both loading test patterns into scan chains and for collecting and compressing test responses, eliminating the need for separate dedicated structures.
Solution Approach 2:
The patent combines the scan chain load function with the PRPG pattern generation function by directly connecting PRPG outputs to scan chain inputs through compression structures. This merging eliminates the need for separate test pattern storage and loading mechanisms, reducing overall device complexity while maintaining compression benefits.
3Productivity
If multiple PRPG instances are used to generate test patterns for different scan chain groups, then test application time is reduced, but device complexity increases
Solution Approach 1:
The patent segments the scan chains into multiple groups, each served by a dedicated PRPG instance. This allows parallel generation and application of test patterns to different scan chain groups simultaneously, significantly reducing total test application time while keeping each PRPG instance relatively simple.
Solution Approach 2:
The patent introduces a new dimension of parallelism by operating multiple PRPG instances simultaneously on different scan chain groups. This multi-dimensional approach to test pattern generation allows concurrent operation rather than sequential processing, improving productivity without requiring each individual PRPG to be overly complex.
Data Source
AI summary
A scan test system and technique compresses CARE bits and X-control input data into PRPG seeds, thereby providing a first compression. The scan test system includes a plurality of compressor and decompressor structures (CODECs). Each block of the design includes at least one CODEC. An instruction decode unit (IDU) receives scan inputs and determines whether a seed extracted from the scan inputs is broadcast loaded in the CODECs, multicast loaded in a subset of the CODECs, or individual loaded in a single CODEC. This sharing of seeds, exploits the hierarchical nature of large designs with many PRPGs, provides a second compression. Results on large industrial designs demonstrate significant data and cycle compression increases while maintaining test coverage, diagnosability, and performance.