Clock Data Recovery Metastable State Exit Phase Interpolator
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Solution Overview
Problem
Receivers in high-speed data communications face challenges in quickly acquiring a clock signal lock from burst mode data packets, often getting stuck in metastable states which prolong lock times and lead to data errors.
Innovation Solution
A method and apparatus that check for metastable states in the clock and data recovery block of a receiver, shifting the phase input to a phase interpolator to exit this state within a limited time by determining phase differences between samples taken at different times and adjusting the phase input by approximately 90 degrees or more increments of a phase interpolator code to ensure rapid lock acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the CDR block operates in burst mode to track each new burst of data, then the receiver can handle short packet transmissions, but the lock time is limited by the preamble length which may be insufficient for proper locking
Solution Approach 1:
The patent applies preliminary action by detecting metastable states before they cause locking failures. The system proactively identifies when the CDR block is approaching a metastable condition and takes corrective phase adjustments in advance, preventing the locking process from stalling and ensuring timely lock acquisition within the limited preamble duration
Solution Approach 2:
The patent changes the phase parameter of the CDR block when a metastable state is detected. By adjusting the phase input to exit the metastable state, the system modifies the operational parameters of the CDR block to achieve proper locking within the constrained time available in burst mode operations
2Reliability
If the CDR block enters a metastable state during burst mode operation, then phase alignment may be achieved, but the lock time is prolonged leading to data errors
Solution Approach 1:
The patent implements feedback by continuously monitoring the CDR block for metastable states and using this information to trigger corrective actions. The system detects when phase alignment is problematic and feeds this information back to adjust the phase input, creating a closed-loop control mechanism that prevents prolonged metastable conditions and ensures timely locking
Solution Approach 2:
The patent converts the harmful metastable state into a beneficial detection opportunity. By monitoring for metastable conditions, the system identifies when phase alignment is occurring and uses this information to make precise corrective adjustments, transforming a potentially harmful state into a useful indicator for optimizing lock acquisition
Data Source
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Figure 3
Figure 4-1~4-4
AI summary
A method (100, 300, 500) relates generally to a receiver (200). In such a method (100), a check (101 ) of a clock and data recovery block (203) of the receiver (200) for a metastable state is performed. A phase input (214) to a phase interpolator (204) of the receiver (200) is changed (102) to cause the clock and data recovery block (203) of the receiver (200) to exit the metastable state within a time limit. To check for the metastable state, a phase difference in received data is determined (111 ), and the phase difference is determined to be less than a threshold (112) for the clock and data recovery block (203) being in the metastable state.