Scan Cell Grouping and Scheduling for Low-Power BIST Coverage
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Solution Overview
Problem
Existing semiconductor test technologies face challenges in achieving high test coverage with a small number of patterns and reducing test power consumption due to increased area and route overhead as the number of scan cells and chains grow.
Innovation Solution
A method involving calculating scan cell weights, dividing them into coverage and power groups, forming power subgroups, and scheduling these subgroups to reduce peak power consumption during the test process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of scan cells and chains is increased to improve test coverage, then test coverage is improved, but area and route overhead increase
Solution Approach 1:
The patent divides scan cells into multiple chains and further segments these chains into groups that can be independently controlled. By segmenting the scan structure, the patent achieves high test coverage through multiple scan chains while reducing the area overhead of combination circuits by allowing selective activation of only necessary chain groups for each test pattern.
Solution Approach 2:
The patent implements dynamic control of scan chains through control registers that can selectively activate or deactivate specific scan chain groups based on the test pattern being applied. This dynamic approach allows the system to adapt the active scan resources to the specific test requirements, improving coverage when needed while reducing area overhead by keeping unnecessary chains inactive.
2Reliability
If the number of scan cells and chains is increased to improve test coverage, then test coverage is improved, but route overhead increase
Solution Approach 1:
By segmenting scan cells into multiple independently controllable chains and groups, the patent reduces route overhead. Each chain group can be activated selectively, meaning that not all scan chains need to be routed and activated simultaneously. This segmentation allows the routing infrastructure to be more efficient, as only the necessary chain groups are activated for each specific test pattern.
Solution Approach 2:
The dynamic control mechanism allows the system to activate only the scan chain groups necessary for each test pattern. This reduces the complexity of routing because the control logic can selectively enable specific chain groups, avoiding the need to route and manage all scan chains simultaneously, thereby reducing overall route overhead.
3Reliability
If deterministic patterns are used to achieve high test coverage, then test coverage is improved, but peak power consumption increases
Solution Approach 1:
The patent divides scan chains into multiple groups that can be independently controlled. During testing, only specific chain groups are activated based on the test pattern requirements. This segmentation allows deterministic patterns to be applied to selected groups rather than all chains simultaneously, thereby achieving high test coverage while distributing and reducing peak power consumption across different time periods and chain groups.
Solution Approach 2:
The patent implements periodic activation of different scan chain groups rather than continuous activation of all chains. By cycling through different chain groups and activating them in a scheduled manner, the system achieves comprehensive test coverage over time while ensuring that peak power consumption is distributed across multiple periods rather than concentrated in a single moment.
Data Source
AI summary
There is provided a scan cell placing method including calculating a weight of each scan cell from a deterministic pattern input to a plurality of scan cells, dividing the scan cells into a coverage group and a power group on the basis of the weights, forming a plurality of power subgroups from a result of providing a pseudo random pattern to scan cells belonging to the power group, and scheduling one or more of the power subgroups to reduce peak power in a test process.