Cross-Coupled Synchronizer Latch for Fast Metastability Resolution
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Synchronizer performance does not scale with logic-gate performance in deep sub-micron technologies, and existing synchronizer circuits based on data-path flip-flops struggle to resolve metastability issues due to design criteria that prioritize low clock-to-Q delay over robustness, leading to increased latency and reliability concerns.
Innovation Solution
A synchronizer latch circuit with lightly loaded, cross-coupled transistors that create a voltage difference between outputs, allowing data and clock inputs to control neighboring power sources and ground connections, amplifying the voltage difference to generate valid logic outputs even when inputs arrive simultaneously, thereby rapidly resolving metastability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If standard data-path flip-flops are used for synchronization, then clock-to-Q delay is minimized, but metastability resolution capability deteriorates
Solution Approach 1:
The synchronizer is divided into two independent stages: a metastability-resolution stage using cross-coupled latches with high gain, and a data-output stage using standard flip-flops. This segmentation allows each stage to be optimized for its specific function without compromise.
Solution Approach 2:
The cross-coupled latches use unequal transistor sizing (different W/L ratios) to create asymmetric gain characteristics that favor rapid metastability resolution. The transistor dimensions are specifically chosen to maximize the restoring force when outputs deviate from equilibrium, enabling fast recovery from metastable states.
2Reliability
If synchronizer robustness is improved through enhanced metastability resolution, then reliability increases, but device complexity increases
Solution Approach 1:
The cross-coupled latch structure serves multiple functions: it acts as a metastability-resolution element, a data storage element, and a signal conditioning stage. By combining these functions in a single unified structure, the design avoids the need for separate dedicated components for each function.
Solution Approach 2:
The design merges the metastability-resolution function with the data-latching function by using the same cross-coupled transistor pair for both purposes. The clocked transistors control both the metastability resolution process and the data transfer timing, eliminating the need for separate resolution and storage circuits.
3Loss of time
If cross-coupled transistors are used to resolve metastability, then metastability resolution speed increases, but power consumption increases
Solution Approach 1:
The cross-coupled latches are clocked periodically, with the clock signal enabling metastability resolution only during specific phases. During other phases, the latches hold their state with minimal power consumption. This periodic operation allows rapid metastability resolution when needed while minimizing power dissipation during stable operation.
Solution Approach 2:
The transistor conductance states are dynamically controlled by clock signals and data inputs. The clocked transistors switch between conducting and non-conducting states, enabling the cross-coupled pair to actively resolve metastability only when required, rather than continuously consuming power to maintain resolution capability.
Data Source
AI summary
The disclosed embodiments provide a synchronizer latch circuit that facilitates resolving metastability issues. This synchronizer latch circuit includes a set of lightly loaded, cross-coupled transistors that form a metastable resolving and state-holding element that is coupled to two outputs. An incoming synchronization signal creates a voltage difference between the two outputs, but does not directly force a state change for the outputs. Instead, the data and clock inputs control transistors that allow neighboring power sources and/or ground network connections to weakly influence the outputs. The cross-coupled transistors then amplify the resulting voltage difference to generate valid output voltages, even when the data input and clock signal are received at roughly the same time. Thus, the synchronizer latch circuit facilitates rapidly resolving metastability and improving synchronizer performance.