DCO Gain Compensation for Stable Multi-Channel PLL 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 cubic nonlinearity of DCO gain, allowing for predictive locking and stable frequency generation without runtime frequency measurement, through a method involving gain estimation, multiplexing, and arithmetic processing to generate an oscillator tuning word.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a DCO is used in an all-digital PLL to reduce area and power dissipation, then area and power consumption are reduced, but nonlinear behavior across the tuning band causes stability issues and uncertainty in PLL performance
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the DCO tuning word based on the detected nonlinear behavior at different frequency points. The system characterizes the nonlinear gain behavior across the tuning band and compensates by modifying the tuning word parameters, thereby maintaining stable PLL performance while using a DCO for reduced power dissipation.
Solution Approach 2:
The patent implements feedback by detecting the actual output frequency of the DCO and comparing it with the expected frequency. Based on the detected error and nonlinear behavior, the system adjusts subsequent tuning words to compensate for the nonlinearity, creating a closed-loop compensation mechanism that stabilizes PLL performance.
2Adaptability or versatility
If the DCO tuning band is extended to cover more frequency ranges, then frequency versatility is improved, but the nonlinear behavior becomes more pronounced and complicates frequency locking
Solution Approach 1:
The patent applies segmentation by dividing the wide tuning band into multiple frequency ranges or channels. For each channel, the system pre-characterizes the nonlinear behavior and stores compensation parameters. When operating in a specific frequency range, the appropriate compensation parameters are selected, simplifying the frequency locking process while maintaining wide frequency versatility.
Solution Approach 2:
The patent implements preliminary action by pre-characterizing the nonlinear behavior of the DCO across the entire tuning band during manufacturing or initialization. The compensation parameters are calculated and stored in advance, so that during normal operation, the system can quickly apply the appropriate compensation without complex real-time calculations, reducing locking complexity.
3Measurement precision
If runtime frequency measurement is implemented to compensate for nonlinearity, then frequency accuracy is improved, but additional measurement and control circuitry increases device complexity
Solution Approach 1:
The patent applies copying by using a simplified model or lookup table that replicates the nonlinear behavior characteristics. Instead of implementing complex real-time frequency measurement and analysis circuitry, the system uses a pre-created copy of the nonlinear behavior data, which can be queried and applied for compensation with minimal additional circuitry.
Solution Approach 2:
The patent implements this principle by using a simplified, low-cost frequency measurement approach that may have limited precision but is sufficient for the compensation purpose. The measurement is performed only when needed for compensation rather than continuously, reducing the complexity and cost of the measurement circuitry while still achieving the required frequency accuracy.
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.