Bidirectional Scan Flip-Flop Circuit for Better DFT Error Detection
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Solution Overview
Problem
Existing circuit designs for integrated circuits (ICs) lack the ability to efficiently detect errors during the design-for-test (DFT) process, particularly due to fixed scan directions which limit the effectiveness of error detection.
Innovation Solution
The introduction of a scan flip-flop circuit with selectable scan directions, incorporating selection circuits and drivers that allow data bits to be propagated in both forward and reverse directions, enhancing error detection capabilities during DFT.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed scan direction is used in the DFT process, then the circuit structure is simple, but the error detection capability is limited
Solution Approach 1:
The patent implements dynamic scan direction control by introducing a direction control signal that can switch between forward and reverse scan directions. The scan chain configuration changes dynamically based on the direction control signal, allowing the same hardware to adapt to different testing requirements and improve error detection capability without permanently increasing circuit complexity.
Solution Approach 2:
The patent changes the scanning parameter (scan direction) to improve error detection. By allowing the scan direction to be changed between forward and reverse modes through control signals, the system can detect errors that might be missed with a fixed scan direction, thereby improving reliability while maintaining relatively simple circuit structure.
2Reliability
If a bidirectional scan capability is added, then the error detection capability is improved, but the device complexity increases
Solution Approach 1:
The patent makes the scan chain multi-functional by enabling it to operate in both forward and reverse directions using the same hardware resources. The bidirectional scan capability allows a single scan chain to perform multiple testing functions, improving error detection without requiring separate scan chains for each direction, thus limiting the increase in device complexity.
Solution Approach 2:
The scan chain is designed to be dynamically reconfigurable, switching between forward and reverse modes based on control signals. This dynamic capability allows the system to achieve bidirectional scanning functionality without permanently duplicating hardware, thereby improving error detection while controlling the increase in circuit complexity.
3Productivity
If bidirectional data propagation is implemented, then test efficiency is enhanced, but the control circuit complexity increases
Solution Approach 1:
The patent implements dynamic control of data propagation direction through direction control signals. The control circuit dynamically switches between forward and reverse propagation modes based on testing requirements, enabling efficient bidirectional testing without requiring permanently complex control logic for both directions simultaneously.
Solution Approach 2:
The control circuit changes the propagation parameter (direction) based on control signals, allowing efficient bidirectional data flow. By changing the propagation direction parameter rather than maintaining fixed bidirectional paths, the control circuit complexity is minimized while still achieving enhanced test efficiency through bidirectional capability.
Data Source
AI summary
A scan flip-flop circuit includes first and second I/O nodes, a flip-flop circuit, a selection circuit configured to receive a scan direction signal and including input terminals coupled to the first and second I/O nodes and an output terminal coupled to an input terminal of the flip-flop circuit, and first and second drivers configured to receive the scan direction signal and a scan enable signal, each including an input terminal coupled to an output terminal of the flip-flop circuit and an output terminal coupled to a respective first or second input terminal of the selection circuit. Responsive to the scan direction and scan enable signals, one of the first driver is configured to output a first signal responsive to a second signal received at the second input terminal or the second driver is configured to output a third signal responsive to a fourth signal received at the first input terminal.