Scannable Data Synchronizer for Metastability-Aware Latching
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Solution Overview
Problem
Conventional methods for latching asynchronous data signals into a clock domain are prone to metastability, which can cause malfunction or circuit failure, especially in high-speed systems, and do not guarantee proper operation across various technologies including FinFET technologies, and they often introduce significant latency or require adjusting transistor size and drive strength.
Innovation Solution
A scannable data synchronizer is developed, comprising an input circuit, pass gates, inverters, and a gate controller that delays latching during metastability and keeps pass gates open until the signal stabilizes, using P-channel and N-channel devices controlled by AND-OR-Invert and OR-AND-Invert gates to ensure proper registration without relying on transistor size adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two registers are coupled in series to reduce metastability probability, then reliability improves, but latency increases and performance decreases
Solution Approach 1:
The gate controller proactively monitors the capture nodes and keeps pass gates open during metastable conditions before the system fails, rather than waiting for failure to occur. This preliminary detection and response mechanism prevents metastability propagation without requiring multiple sequential registers, thus maintaining low latency while improving reliability
2Reliability
If additional registers are added in series to further reduce failure probability, then reliability improves, but latency increases significantly
Solution Approach 1:
The gate controller acts as an intermediary between the capture nodes and the pass gates, monitoring the voltage states of capture nodes and dynamically controlling pass gate openness. This intermediary mechanism enables real-time detection and resolution of metastability conditions, achieving high reliability without the latency penalty of multiple sequential registers
3Difficulty of detecting and measuring
If transistor size and drive strength are adjusted to detect metastability, then detection capability improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The gate controller detects metastability by monitoring voltage parameter changes at the capture nodes rather than relying on transistor size adjustments. By changing the detection parameter from physical transistor dimensions to electrical voltage levels, the system achieves effective metastability detection while reducing manufacturing complexity and improving adaptability to different technology nodes
4Productivity
If the system operates faster, then productivity improves, but the likelihood of metastability increases
Solution Approach 1:
The gate controller implements a feedback mechanism by continuously monitoring the voltage states of capture nodes and dynamically adjusting pass gate control signals based on detected conditions. This feedback loop enables the system to operate at high speeds while automatically detecting and resolving metastability events, thus maintaining both high productivity and reliability
Data Source
AI summary
A scannable data synchronizer including an input circuit, first and second pass gates, first and second inverters, and a gate controller. The input circuit drives the data nodes to opposite logic states in response to an asynchronous input data signal in a normal mode and in response to scan data in a scan test mode. Each pass gate is coupled between one of the data nodes and a corresponding one of the capture nodes, and each has at least one control terminal. The inverters are cross-coupled between the second capture nodes. The gate controller can keep the pass gates at least partially open during a metastable condition of the capture nodes, and can close the pass gates when both capture nodes stabilize to opposite logic states. In the scan test mode, the scan data is used to test the latch or register functions of the scannable data synchronizer.