TOD Clock-Domain Interface With Phase-Guided Resynchronization
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Solution Overview
Problem
Existing systems face inaccuracies when transferring Time of the Day (TOD) data across asynchronous clock domains due to asynchronous clocks leading to incorrect sampling during clock transitions.
Innovation Solution
A clock domain interface circuit that includes a phase detector to determine phase differences, a sample conditioner to synchronize TOD words based on a second clock while discarding unsynchronized samples, and an interpolator to fill gaps in the synchronized TOD words.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If TOD words are sampled directly from asynchronous clock domains, then the sampling operation is simple and fast, but sampling may occur during clock transitions leading to inaccurate TOD data
Solution Approach 1:
The phase detector performs preliminary detection of the phase difference between clock domains before the sampling operation. This advance knowledge allows the system to determine whether sampling should proceed or be deferred, preventing inaccurate sampling during clock transitions while maintaining efficient operation when conditions are favorable.
Solution Approach 2:
The phase detector acts as an intermediary between the asynchronous clock domains and the sampling circuitry. It provides critical phase difference information that mediates the sampling decision, ensuring that TOD data is only sampled when the timing relationship between clocks guarantees accurate capture, thus resolving the contradiction between simple sampling and accurate sampling.
2Measurement precision
If TOD words are discarded when phase difference does not meet timing margin, then sampling accuracy is improved, but gaps appear in the re-synchronized TOD word sequence
Solution Approach 1:
The interpolator creates copies of valid TOD words and modifies them to fill the gaps caused by discarded samples. By generating synthetic TOD values based on the phase difference information and adjacent valid samples, the system restores continuity to the TOD word sequence while preserving the accuracy improvements gained from selective discarding.
Solution Approach 2:
The interpolator changes the parameters of existing TOD words (their temporal values) to create synthetic fill-in values that match the expected TOD sequence. By adjusting these parameters based on phase difference calculations, the system maintains both the accuracy benefits of discarding bad samples and the continuity required for TOD applications.
3Measurement precision
If phase detection and conditional sampling circuitry are added, then TOD data accuracy across asynchronous domains is improved, but device complexity increases
Solution Approach 1:
The phase detector serves multiple functions: it detects phase difference between clock domains, provides timing margin information for sampling decisions, and enables the interpolator to generate accurate fill-in values. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby limiting the increase in device complexity while achieving improved cross-domain TOD accuracy.
Data Source
AI summary
Methods to move Time of the Day (TOD) across asynchronous clock domains with no loss in accuracy include receiving time-of-day (TOD) words that are synchronized to a first clock, estimating a phase difference between the first clock and a second clock, sampling the TOD words based on the second clock to provide re-synchronized TOD words that are synchronized to the second clock, when the phase difference meets a timing margin, discarding the TOD words when the phase difference does not meet the timing margin, and interpolating the re-synchronized TOD words to fill gaps in the re-synchronized TOD words that correspond to the discarded TOD words. The methods may further include adjusting values of the re-synchronized TOD words based on magnitudes of the corresponding phase differences.