Data Synchronization Circuit With Metastability Masking
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Solution Overview
Problem
Metastability in data synchronization leads to unreliable circuit operations due to flip-flops entering invalid logic states, causing lingering or incorrect output signals, which conventional serial chaining of flip-flops only mitigates rather than addressing the root cause and adds power consumption and delay.
Innovation Solution
An apparatus comprising a sampling circuit, a masking circuit, and a sync circuit that samples data input signals at rising and falling edges of a latching signal, delays signals to prevent metastability by selectively masking transitions, and synchronizes data without entering metastable conditions, using delay circuits and masking logic to ensure valid logic levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If serial chaining of flip-flops is used to mitigate metastability consequences, then reliability is improved, but power consumption increases and signal delay increases
Solution Approach 1:
A delay circuit is introduced as an intermediary element between the first and second flip-flops. This delay circuit selectively delays the output signal from the first flip-flop based on detected metastable conditions, preventing the propagation of invalid logic levels to the second flip-flop. The intermediary delay mechanism resolves the contradiction by providing metastability protection without requiring the second flip-flop to be continuously chained, thereby reducing power consumption and signal delay while maintaining reliability.
2Reliability
If serial chaining of flip-flops is used to mitigate metastability consequences, then reliability is improved, but device complexity increases
Solution Approach 1:
The delay circuit acts as a mediator that simplifies the overall circuit architecture by replacing the need for complex metastability detection and correction logic in serially chained flip-flops. Instead of requiring multiple flip-flops to be continuously chained with complex control logic, the delay circuit provides a simpler mechanism that selectively delays signals only when metastability is detected, thereby reducing device complexity while maintaining reliability improvements.
3Reliability
If serial chaining of flip-flops is used to mitigate metastability consequences, then reliability is improved, but signal delay increases
Solution Approach 1:
The delay circuit serves as an intermediary that introduces minimal, selective delay only when metastable conditions are detected. Unlike serial chaining of multiple flip-flops that inherently introduces cumulative delay through each stage, the delay circuit provides a controlled, single-stage delay mechanism that activates only when necessary. This approach maintains reliability by preventing metastability propagation while minimizing signal delay loss.
4Speed
If flip-flop latches input signal without sufficient charging/discharging time, then speed is improved, but metastability occurs
Solution Approach 1:
The delay circuit performs a preliminary action by detecting metastable conditions and selectively delaying the output signal from the first flip-flop before it reaches the second flip-flop. This preliminary intervention prevents invalid logic levels from propagating through the circuit, thereby maintaining reliability without requiring the flip-flop to slow down its latching operation. The preliminary delay action resolves the contradiction by protecting against metastability consequences while preserving high-speed latching performance.
Data Source
AI summary
Apparatuses, circuits, and methods are disclosed for reducing or eliminating unintended operation resin ling from metastability in data synchronization. In one such example apparatus, a sampling circuit is configured to provide four samples of a data input signal. A first and a second of the four samples are associated with a first edge of a latching signal, and a third and a fourth of the four samples are associated with a second edge of the latching signal. A masking circuit is configured to selectively mask a signal corresponding to one of the four samples responsive to the four samples not sharing a common logic level. The masking circuit is also configured to provide a decision signal responsive to selectively masking or not masking the signal.