Programmable Scan Chain Segmentation for Power Reduction
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Solution Overview
Problem
As the size and complexity of integrated circuits increase, scan chain testing becomes increasingly difficult due to high power draw and challenges in identifying fault locations, with existing methods often exceeding normal functional power expectations and risking chip damage from excessive toggling activity.
Innovation Solution
The implementation of a programmable scan chain testing method that includes a first segment of scan-flops connected in series with a second segment, where a multiplexor selectively supplies test controller inputs to the second segment while preventing output from the first segment, allowing for selective isolation and reduced toggling activity without decreasing fault coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a complete scan chain tests all cells in sequence, then fault coverage is improved, but power draw exceeds normal functional expectations
Solution Approach 1:
The scan chain is divided into multiple segments with scan-flops grouped together. Multiplexors are inserted between segments to enable selective activation. During testing, only necessary segments are activated while others remain inactive, reducing overall power consumption while maintaining adequate fault coverage for the activated portions.
Solution Approach 2:
Instead of activating the entire scan chain for every test, the invention enables partial activation where only specific segments are tested based on test requirements. This partial action approach reduces power draw by avoiding unnecessary toggling in segments that don't need testing, while still achieving sufficient fault coverage for the critical areas being tested.
2Reliability
If all scan-flops are toggled during testing, then fault coverage is improved, but the risk of chip damage from excessive toggling activity increases
Solution Approach 1:
By segmenting the scan chain into multiple groups controlled by separate multiplexors, the invention limits toggling activity to only the segments that are currently being tested. This segmentation prevents excessive toggling across the entire chain, reducing heat generation and stress on individual cells, thereby lowering the risk of chip damage while maintaining adequate fault coverage for the active segments.
3Reliability
If the entire scan chain is tested as one unit, then testing completeness is improved, but debugging difficulty increases due to inability to isolate fault locations
Solution Approach 1:
The scan chain is segmented into multiple groups with multiplexors positioned between them. During testing, individual segments can be activated or deactivated by controlling the multiplexor select lines. When a fault is detected, the segmented structure allows testers to isolate and re-test specific segments to pinpoint the fault location, significantly improving debugging efficiency while maintaining complete testing coverage across all segments.
Solution Approach 2:
Multiplexors act as intermediary elements between scan-flop segments. These multiplexors enable selective connection of segments to the test controller, allowing individual segments to be tested in isolation or in combination. This intermediary structure facilitates fault isolation by enabling the test controller to activate only the segment containing the suspected fault, making debugging much more efficient.
4Reliability
If scan chain testing is performed on large integrated circuits, then test coverage is improved, but test complexity increases
Solution Approach 1:
The scan chain is divided into multiple segments with multiplexors controlling each segment's activation. This segmentation transforms a single complex test sequence for the entire chain into multiple simpler, independent test sequences for individual segments. The test controller can manage each segment separately, reducing the overall test sequence complexity while maintaining comprehensive coverage across all segments through systematic activation and deactivation.
Data Source
AI summary
The disclosed technology facilitates programmable scan shift testing for a scan chain including at least a first segment of scan-flops connected in series with a second segment of scan-flops. The scan chain includes at least a first multiplexor positioned between the first segment and the second segment that is configured to selectively supply scan input from a test controller to the second segment while preventing the second segment from receiving an output of the first segment.