Charge-Sharing DCO Locking for Low-Error PLL Phase Tracking
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Solution Overview
Problem
Phase locked loops (PLLs) in circuits face challenges in generating high-frequency signals with reduced phase and frequency errors, particularly in applications requiring precise phase tracking and frequency synthesis, such as radio receivers and digital communication systems.
Innovation Solution
Implementing a ring based digitally controlled oscillator (DCO) coupled with a charge-sharing circuit that includes a charge-sharing capacitor, switch, and a digital-to-analog converter (DAC), which adjusts the closed loop transfer function of the PLL to reduce phase and frequency errors through charge-sharing corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional PLL is used to generate high-frequency signals, then frequency synthesis capability is provided, but phase and frequency errors increase
Solution Approach 1:
The patent implements a feedback mechanism where the oscillating signal from the DCO is fed back through the charge-sharing circuit to the input of the DCO. The charge-sharing circuit compares the phase and frequency of the oscillating signal with reference signals and adjusts the control voltage accordingly, creating a closed-loop system that continuously corrects phase and frequency errors to improve precision
Solution Approach 2:
The patent replaces traditional mechanical or analog phase-locked loop mechanisms with a digitally controlled oscillator system. The DCO uses digital control signals to adjust the oscillation frequency and phase, substituting digital electronics for conventional analog circuitry, which enables more precise and programmable control of phase and frequency parameters
2Measurement precision
If the closed loop transfer function of the PLL is modified to reduce phase and frequency errors, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent introduces a charge-sharing circuit as an intermediary component between the DCO and the reference signals. This circuit shares the control voltage between different parts of the PLL system and provides smooth transitions during phase and frequency adjustments, reducing complexity by avoiding the need for separate control circuits for each function
Solution Approach 2:
The charge-sharing circuit performs multiple functions simultaneously: it controls the oscillation frequency of the DCO, adjusts the phase of the oscillating signal, and provides feedback for error correction. This multi-functionality reduces the overall number of components needed in the PLL system, thereby reducing device complexity while maintaining improved precision
Data Source
AI summary
A method includes causing a digital controlled oscillator to oscillate in a phase locked loop having a first closed loop transfer function, and changing the phase locked loop having the first closed loop transfer function to a phase locked loop having a second closed loop transfer function. The method also includes starting a charge-sharing locking process to correct phase errors in the digital controlled oscillator while the digital controlled oscillator oscillates in the phase locked loop having the second closed loop transfer function.