Scan Test Circuit Bypassing Confidential Sub-Chains
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Solution Overview
Problem
Existing scan test circuits for semiconductor integrated circuits face challenges in testing high confidentiality-requiring circuits while maintaining security and minimizing overhead, as they often require additional compression or encryption circuits, leading to increased processing and circuit area, and are not designed for failure analysis in non-compression modes.
Innovation Solution
A scan test circuit and method that utilizes a scan chain with sub-scan chains, an input distribution circuit, and an output compression circuit to switch between compression and non-compression modes, bypassing high confidentiality-requiring circuits in non-compression mode to protect confidentiality and connecting them in compression mode for thorough testing, using existing input distribution and output compression circuits to minimize overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a scan test circuit uses non-compression scan mode to directly read out output signals from scan cell circuits, then test quality and observability are improved, but security confidentiality is compromised
Solution Approach 1:
The patent applies dynamics by making the scan chain configuration changeable between two states: connected mode (for testing non-confidential circuits) and bypassed mode (for confidential circuits). The scan enable signal dynamically controls whether scan cell circuits are included in the scan chain, allowing the system to adapt its structure based on security requirements while maintaining test capability.
Solution Approach 2:
The patent applies local quality by treating different circuits differently within the same scan test system. Confidential circuits are excluded from the scan chain (bypassed) while non-confidential circuits are included, allowing selective application of scan testing based on the security sensitivity of individual circuit regions.
2Loss of information
If a scan test circuit excludes high confidentiality-requiring circuits from testing to protect security, then security confidentiality is maintained, but test quality and failure detection capability are reduced
Solution Approach 1:
The patent enables dynamic switching between including and excluding confidential circuits from the scan chain based on the scan enable signal. When the signal indicates non-confidential circuits, the full scan chain is active for comprehensive testing. When confidential circuits are detected, they are bypassed while maintaining scan chain functionality for other circuits, thus balancing security and test quality.
Solution Approach 2:
The patent applies local quality by selectively applying different scan chain configurations to different circuit regions. Confidential circuits receive the bypass treatment while non-confidential circuits receive full scan chain testing, allowing the system to optimize both security and test quality locally rather than applying a uniform approach globally.
3Loss of information
If a scan test circuit uses compression scan mode to compress output signals, then security confidentiality is improved, but test quality and failure analysis capability are reduced
Solution Approach 1:
The patent applies dynamics by dynamically switching between compression scan mode (for security) and non-compression scan mode (for test quality) based on the type of circuit being tested. The scan enable signal controls whether output signals are compressed or directly observed, allowing the system to adapt its observation method to the security requirements of the underlying circuit.
Solution Approach 2:
The patent applies local quality by applying different output signal handling methods to different circuit regions. Confidential circuits use compression scan mode to protect security, while non-confidential circuits use non-compression mode for comprehensive test quality, allowing each region to be treated according to its specific security requirements.
4Loss of information
If a scan test circuit adds dedicated compression circuits and encryption circuits for high confidentiality-requiring circuits, then security confidentiality is improved, but device complexity and overhead are increased
Solution Approach 1:
The patent applies universality by making the existing scan chain structure multi-functional. The same scan chain infrastructure serves both confidential and non-confidential circuits, with the scan enable signal controlling the configuration. This eliminates the need for separate dedicated compression or encryption circuits, as the existing scan mechanism is adapted to handle both security requirements and test quality requirements through dynamic reconfiguration.
Solution Approach 2:
The patent applies self-service by using the existing scan chain structure to provide its own security functionality through the bypass mechanism. Rather than requiring external compression or encryption circuits, the scan chain itself provides security by selectively bypassing confidential circuits, thus serving its own security needs without additional dedicated hardware.
Data Source
AI summary
A scan test circuit includes a scan chain formed of a plurality of sub-scan chains, an input distribution circuit, and an output compression circuit. With the use of a bypass circuit, a plurality of sub-scan chains are formed in a compression scan mode by connecting scan cell circuits of a high confidentiality-requiring circuit among a plurality of scan cell circuits included in an internal circuit, and a plurality of sub-scan chains are formed in a non-compression scan mode by bypassing the scan cell circuits of the high confidentiality-requiring circuit.