DCO Gain Compensation for Stable Wideband ADPLL Channel Hopping
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Solution Overview
Problem
Digitally controlled oscillators (DCOs) exhibit nonlinear behavior across their tuning band, leading to stability issues and uncertainty in phase locked loop (PLL) performance, particularly in all-digital PLLs (ADPLLs), which complicates frequency locking and signal generation.
Innovation Solution
The implementation of a compensation technique using a normalizing gain multiplier to address the nonlinear DCO gain, specifically through cubic rule compensation and center linear interpolation, allows for predictive locking and stable frequency generation without runtime frequency measurement, reducing phase error and improving locking speed and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If DCO operates across wide tuning band, then frequency range is improved, but nonlinear gain behavior causes stability issues and performance uncertainty
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the gain value of the DCO based on the tuning word input. A lookup table stores pre-calibrated gain values corresponding to different frequency ranges, and the system selects appropriate gain values based on the current operating point. This compensates for the nonlinear gain behavior across the tuning band, maintaining stability while enabling wide frequency range operation.
2Speed
If DCO gain is increased for faster locking, then locking speed is improved, but phase error increases due to nonlinear behavior
Solution Approach 1:
The patent dynamically changes the gain parameter based on the current tuning word and frequency range. The lookup table provides optimized gain values that balance locking speed and phase accuracy for different operating conditions. By selecting appropriate gain values from the lookup table rather than using a fixed or linearly scaled gain, the system achieves fast locking without excessive phase error.
Solution Approach 2:
The system uses feedback from the phase detector and frequency information to adjust the DCO gain. The lookup table is indexed based on the current tuning word and measured frequency, creating a closed-loop system that adapts the gain to maintain optimal performance. This feedback mechanism ensures that the gain is optimized for the current operating point, reducing phase error while maintaining locking speed.
3Device complexity
If linear interpolation is used to simplify gain calculation, then device complexity is reduced, but accuracy deteriorates due to cubic nonlinear behavior
Solution Approach 1:
The patent performs preliminary action by pre-calculating and storing accurate gain values in a lookup table during the design or calibration phase. These pre-computed values account for the cubic nonlinear behavior of the DCO. During operation, the system simply retrieves the appropriate gain value from the lookup table based on the tuning word, avoiding the need for complex real-time calculations while maintaining high accuracy.
Solution Approach 2:
The system creates a digital copy of the DCO gain characteristics in the form of a lookup table. Instead of directly computing the complex nonlinear gain relationship in real-time, the patent uses a pre-recorded representation (the lookup table) that replicates the actual DCO behavior. This copied model allows for fast retrieval and simple indexing operations while preserving the accuracy of the nonlinear characteristics.
Data Source
AI summary
Systems and methods are provided for hopping a digitally controlled oscillator (DCO) among a plurality of channels, wherein a gain of the DCO KDCO is a nonlinear function of frequency. A first normalized tuning word (NTW) corresponding to a first channel of the plurality of channels is generated. A first normalizing gain multiplier X is generated based on the nonlinear function of frequency, on an estimate of the nonlinear function of frequency, at a first frequency corresponding to the first channel. The first NTW is multiplied by the first X to obtain a first oscillator tuning word (OTW). The first OTW is input to the DCO to cause the DCO to hop to the first channel. A system for hopping among a plurality of channels at a plurality of respective frequencies comprises a phase-locked loop (PLL), a digitally controlled oscillator (DCO), a multiplexer, and an arithmetic module.