Cascade VCO Current Control for Low-Jitter PLL Frequency Tuning
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Solution Overview
Problem
Conventional voltage controlled oscillators (VCOs) in phase lock loop (PLL) circuits exhibit high gain and sensitivity to noise, leading to increased jitter in output frequency, which affects the overall performance of the PLL.
Innovation Solution
A VCO with a cascade chain of oscillation units and current source sections, including a fixed current source using a reference direct-current voltage and a variable current source, reduces the gain and sensitivity by stabilizing the output frequency through coarse and fine tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional VCO with high gain is used to achieve frequency tuning, then the frequency response is sensitive to control voltage, but the output frequency becomes highly sensitive to noise causing increased jitter
Solution Approach 1:
The VCO is divided into multiple oscillation units connected in cascade, where each unit contributes to the overall frequency response. This segmentation allows the system to maintain fast response while reducing the impact of noise on any single unit, thereby lowering overall jitter.
Solution Approach 2:
Different current source sections are assigned to different oscillation units, with each section providing localized current control. This allows optimized current distribution across the oscillation chain, enabling fast frequency response in some sections while maintaining stability in others.
2Adaptability or versatility
If the control voltage is changed to adjust the output frequency, then the frequency can be tuned, but small voltage changes cause large frequency variations due to high gain
Solution Approach 1:
The VCO employs dynamic current control through multiple current source sections that can be independently adjusted. This dynamic control mechanism allows for both coarse and fine frequency tuning while maintaining stable operation, reducing the sensitivity to small voltage changes.
Solution Approach 2:
The invention changes the control parameter from direct voltage control to current control through multiple current source sections. By using fixed and variable current sources in combination, the system achieves wide frequency tuning range while improving frequency control precision and reducing jitter.
3Device complexity
If a simple inverter chain VCO structure is used, then the device complexity is low, but the gain is high causing increased sensitivity to noise and jitter
Solution Approach 1:
The simple inverter chain is segmented into multiple oscillation units, each with its own current source section. This maintains relatively low complexity while distributing the noise sensitivity across multiple units, reducing the overall impact of noise on the output frequency.
Solution Approach 2:
Current source sections are introduced as intermediary elements between the control voltage and the oscillation units. These current sources act as buffers that reduce the direct coupling between control voltage noise and the oscillation frequency, thereby reducing noise sensitivity while maintaining structural simplicity.
Data Source
AI summary
A Voltage Controlled Oscillator (VCO) includes a plurality of oscillation units connected in cascade to form a chain; and a plurality of current source sections operatively connected to the oscillation units, the current source sections each being configured to control current provided to the oscillation units, wherein each of the current source sections includes: at least one fixed current source configured to perform a current control of a corresponding oscillation unit by using a fixed voltage; and at least one variable current source configured to perform a current control of the corresponding oscillation unit by using a variable voltage.