Phase Interpolator Rollover Correction for Lower Deterministic Jitter
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Solution Overview
Problem
Phase interpolators in frequency synthesizers face significant integral non-linearity errors due to rollover events, which cannot be effectively calibrated using existing methods without significant complexity and hardware cost, leading to deterministic jitter.
Innovation Solution
A circuit that detects rollover events in phase interpolators and applies signed predistortion corrections to the VCO clock cycle phase fraction values, pre-correcting for integral non-linearity distortion by modifying phase values at consecutive cycles following a rollover event.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If phase interpolators are used in frequency synthesizers to divide VCO clock by fractional divisors, then frequency synthesis capability is improved, but integral non-linearity errors and deterministic jitter increase due to rollover events
Solution Approach 1:
The patent applies preliminary action by detecting rollover events in advance and pre-distorting the phase fraction values before they are used in the phase interpolator. The correction circuit modifies the phase fraction values proactively based on detected rollover conditions, preventing the integral non-linearity errors from occurring in the first place rather than correcting them after they occur
Solution Approach 2:
The patent implements feedback by using the cumulative phase integer value as a feedback signal to detect rollover events. The detector monitors the cumulative phase integer value and uses this information to trigger correction actions, creating a closed-loop system that continuously monitors and corrects phase interpolation errors
2Measurement precision
If calibration methods are applied to correct integral non-linearity errors in phase interpolators, then phase interpolation accuracy is improved, but device complexity and hardware cost increase significantly
Solution Approach 1:
The patent extracts and corrects only the specific component of error related to rollover events rather than attempting to calibrate all phase interpolator errors. By isolating and addressing only the rollover-induced integral non-linearity errors through predistortion, the solution avoids the need for comprehensive and complex calibration hardware while effectively correcting the dominant source of error
Solution Approach 2:
The system performs self-correction by using its own cumulative phase integer value as the basis for detecting rollover events and generating correction signals. The phase interpolator system monitors itself and automatically applies predistortion corrections without requiring external calibration equipment or additional complex calibration circuitry
3Reliability
If rollover events are detected and correction is applied to phase fraction values, then deterministic jitter is reduced, but circuit complexity increases due to detection and correction circuits
Solution Approach 1:
The patent merges the correction circuit with the existing phase interpolator structure by integrating the detector and correction logic into the existing fractional-N synthesizer architecture. The correction is applied by modifying the existing phase fraction values through simple addition or selection logic rather than requiring separate independent correction systems, thereby reducing overall circuit complexity
Data Source
AI summary
A circuit for correcting phase interpolator rollover integral non-linearity errors includes a rollover detector circuit for detecting when a rollover event of a phase interpolator has occurred, and a correction circuit that adds a signed predistortion correction to a VCO clock cycle phase fraction value when the rollover detector circuit has detected the interpolator rollover event.