Reversible Multi-Bit Scan Cell Architecture for Diagnostic Resolution
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Solution Overview
Problem
Conventional scan chain diagnosis techniques face challenges in accurately identifying defective scan cells, especially for un-modeled faults in logic test chips, which can lead to reduced diagnostic accuracy and resolution, and require additional hardware or complex algorithms.
Innovation Solution
The implementation of a scan architecture using multi-bit flip-flops capable of bi-directional scan shifting, with new scan enable signal generation circuitry and multiplexers that allow for reversible scan chains, enabling efficient capture and shift operations in both normal and reverse directions, reducing the number of suspect scan cells and improving diagnostic resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional scan chain diagnosis techniques are used, then the diagnostic process is simple, but the diagnostic accuracy and resolution are reduced for un-modeled faults
Solution Approach 1:
The patent applies bidirectional scan shifting, which reverses the conventional unidirectional approach. By enabling scan chains to shift in both forward and reverse directions, the system can trace defects from multiple directions, significantly improving diagnostic accuracy for un-modeled faults without requiring complex additional hardware
2Measurement precision
If hardware-based methods with specially-designed scan chains are used, then defective scan cells can be isolated, but extra hardware is required
Solution Approach 1:
The patent makes existing scan chains multi-functional by enabling bidirectional operation. The same scan chain infrastructure can perform both conventional unidirectional testing and enhanced bidirectional diagnosis, eliminating the need for specially-designed scan chains or additional hardware while maintaining defect isolation capability
3Measurement precision
If bidirectional scan shifting is implemented, then the number of suspect scan cells is reduced, but the scan chain architecture becomes more complex
Solution Approach 1:
The patent introduces dynamic control signals (scan direction control and new scan enable) that allow the scan chain to flexibly switch between forward and reverse shifting modes. This dynamic architecture enables enhanced diagnostic resolution by reducing suspect scan cells through bidirectional analysis, while the complexity is managed through systematic control signal design rather than structural overhead
Data Source
AI summary
A circuit comprises a scan chain comprising one or more multi-bit flip-flops, a plurality of multiplexers, and new scan enable signal generation circuitry. Each of the plurality of multiplexers is associated with a particular bit of the one or more multi-bit flip-flops with an output of the each of the plurality of multiplexers coupled to a data input of the particular bit, which is configured to select, based on a scan direction control signal, between an input signal from functional circuitry of the circuit and an input signal from a data output of a bit of the scan chain immediately following the particular bit in a normal scan shift direction. The new scan enable signal generation circuitry is configured to generate a new scan enable signal for the one or more multi-bit flip-flops based on the scan direction control signal and a scan enable signal for the scan chain.