PLL Frequency Locking Circuit Using Newton Iteration
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Solution Overview
Problem
Conventional phase-locked loops require a long locking time and suffer from increased phase noise with higher frequency resolution, limiting their efficiency in digital RF circuit design.
Innovation Solution
A frequency locking method and circuit that utilizes a frequency control module, numerically controlled oscillator, and time-to-digital converter to apply the Newton's iterative method for calculating frequency control words, reducing locking time by using ideal frequency control curves and minimizing phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the voltage-controlled gain of the LC voltage-controlled oscillator is increased to reduce locking time, then the locking time decreases, but the phase noise increases significantly
Solution Approach 1:
The frequency locking process is divided into two distinct stages: coarse tuning and fine tuning. The coarse tuning stage uses a frequency control module to quickly achieve approximate frequency alignment, while the fine tuning stage uses a time-to-digital converter to precisely eliminate frequency offsets. This segmentation allows the system to achieve fast locking without excessive phase noise by using different control mechanisms for different phases of the locking process.
Solution Approach 2:
The system dynamically switches between different frequency control modes based on the locking stage. During coarse tuning, the frequency control module operates with higher gain for rapid frequency acquisition. During fine tuning, the time-to-digital converter provides precise, low-noise frequency correction. This dynamic adaptation allows the system to optimize both locking speed and phase noise performance at different stages.
2Measurement precision
If the iteration of frequency control word is increased to improve frequency accuracy, then the frequency accuracy increases, but the time consumption grows
Solution Approach 1:
The frequency control module performs preliminary frequency adjustment during the coarse tuning stage, bringing the oscillator frequency close to the target frequency before the fine tuning stage begins. This preliminary action reduces the frequency offset that needs to be corrected in the subsequent fine tuning stage, thereby reducing the number of iterations required by the time-to-digital converter and decreasing overall time consumption while maintaining high frequency accuracy.
Solution Approach 2:
The frequency control module acts as an intermediary between the initial frequency setting and the final precise frequency control. It performs the bulk of the frequency adjustment work during coarse tuning, reducing the burden on the time-to-digital converter during fine tuning. This intermediary role allows the system to achieve high frequency accuracy with fewer iterations in the critical fine tuning stage.
Data Source
AI summary
A frequency locking method for a phase-locked loop comprises the following steps: S1, a frequency control module controls a numerically controlled oscillator to obtain an maximum output frequency and a minimum output frequency; S2, obtain a minimum frequency ratio and a maximum frequency ratio by means of a time-to-digital converter and the frequency control module; S3, calculate a first frequency control word and a first frequency ratio according to the minimum frequency ratio and the maximum frequency ratio; S4, the frequency control module uses the Newton's iterative method to recalculate a new frequency control word; S5, obtain a new frequency ratio according to the new frequency control word; S6, if the new frequency ratio is within an error range, end iteration and stably output the new frequency control word, and otherwise, jump to step S4.