DPLL Open-Loop Coarse Tuning for Faster Locking and Temperature Compensation
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Solution Overview
Problem
Phase-locked loop (PLL) circuits face challenges in achieving fast settling times and wide temperature coverage due to non-linear coarse tuning fields and limited range of fine tuning fields, leading to increased locking times and complex temperature compensation algorithms.
Innovation Solution
The introduction of a second linear open-loop coarse tuning field parallel to the first non-linear coarse tuning field allows for pre-characterization and reduces the need for multiple frequency measurements during PLL power-up, enabling faster locking and simplified temperature compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a binary successive approximation algorithm or fast band selection algorithm is used for initial DCO frequency setting, then the coarse tuning can be achieved, but the locking time increases due to needing two or more frequency measurements during PLL power up
Solution Approach 1:
The patent pre-calculates and stores lookup tables containing frequency-to-coarse-tuning mappings during chip fabrication or initialization. During PLL operation, the frequency measurement result is directly mapped to the coarse tuning value using these pre-computed tables, eliminating the need for iterative binary search or multiple measurements during power-up.
Solution Approach 2:
The patent creates a simplified model or lookup table that copies the essential frequency-tuning relationship characteristics. Instead of performing complex real-time calculations, the system uses pre-stored mapping data that replicates the frequency-to-tuning correspondence, enabling fast direct lookup without iterative measurements.
2Adaptability or versatility
If the fine tuning field is used for temperature compensation, then the operating point can be adjusted, but the temperature range coverage is limited due to the restricted tuning range of the fine tuning field
Solution Approach 1:
The patent divides the temperature compensation function into two segments: the coarse tuning field handles large-scale temperature drift compensation by providing wide-range frequency adjustment, while the fine tuning field handles precise operating point adjustment within a limited range. This segmentation allows the system to cover the full temperature range while maintaining compensation precision.
Solution Approach 2:
The patent changes the operational parameters of the tuning fields based on temperature conditions. The coarse tuning field is activated for large temperature variations to provide sufficient tuning range, while the fine tuning field is used for smaller adjustments. This dynamic parameter switching enables wide temperature coverage without sacrificing compensation accuracy.
3Reliability
If the coarse tuning field is designed with overlaps to accommodate capacitor mismatches, then frequency continuity is maintained, but the tuning characteristic becomes non-linear increasing algorithm complexity
Solution Approach 1:
The patent pre-calculates and stores lookup tables that account for the non-linear tuning characteristics and capacitor mismatches. During operation, the system performs a simple table lookup based on the measured frequency, avoiding the need for complex real-time algorithms to handle the non-linearity introduced by overlaps.
Solution Approach 2:
The patent creates a simplified mapping model that copies the essential frequency-tuning relationship including the effects of overlaps and mismatches. This pre-computed mapping table replicates the complex non-linear behavior, allowing the system to handle frequency continuity requirements through simple lookup rather than complex algorithms.
Data Source
AI summary
A digital phase-locked loop has a digitally controlled oscillator with a first coarse tuning field for coarse tuning of the oscillator frequency, a second coarse tuning field for tuning of the oscillator frequency at finer intervals than the first coarse tuning field, and a fine tuning field for tuning the oscillator to an output frequency at finer intervals than the second coarse tuning field. The second coarse tuning field provides open loop tuning and is linear and connected parallel to the first coarse tuning field. The second coarse tuning field provides wide field temperature compensation and frequency error determination at start up based on an interpolated frequency value obtained prior to start up. Faster settling is provided with less complex algorithms.