Shared-Varactor Multi-Path VCO for Stable PLL Bias Tracking
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Solution Overview
Problem
Conventional dual-path voltage-controlled oscillators (VCOs) face issues with electromagnetic interference and loop stability due to separate varactors for the integral and proportional paths, which fail to maintain a stable ratio of gains over process, voltage, and temperature variations, leading to poor matching and DC bias tracking.
Innovation Solution
A multi-path VCO design that shares a single varactor among different paths, utilizing time-division multiplexing of control voltages from integral and proportional paths to maintain a stable damping factor and reduce electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If separate varactors are used for I-path and P-path in conventional dual-path VCO design, then bandwidth control and frequency control can be implemented independently, but size disparity causes bad matching and inability to track the same DC bias under PVT variation
Solution Approach 1:
The patent merges the I-path varactor and P-path varactor into a single shared varactor. The control voltage generator receives both I-path control voltage and P-path control voltage, combines them through adder circuits, and applies the combined signal to the shared varactor. This eliminates size disparity and ensures both paths track the same DC bias under PVT variation, resolving the matching issue while maintaining independent control capability through separate control voltage inputs.
2Object-affected harmful factors
If a large I-path gain Ki is used to suppress electromagnetic coupling, then EM suppression improves, but PLL loop stability deteriorates
Solution Approach 1:
The patent changes the control parameters by introducing separate I-path control voltage and P-path control voltage that are combined to control the shared varactor. The P-path control voltage specifically adjusts the damping factor and can be tuned to optimize the Kp/Ki ratio. This allows the system to maintain large I-path gain for EM suppression while using P-path adjustment to restore PLL loop stability, effectively decoupling the two conflicting requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The shared varactor design ensures stable operation over process, voltage, and temperature variations, improving loop stability and reducing electromagnetic interference by maintaining consistent DC bias.
Implementation Method 1
A VCO used in a PLL may be implemented by an inductor-capacitor (LC) VCO
Data Source
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AI summary
A multi-path voltage-controlled oscillator (VCO) includes a VCO core circuit and a control voltage generator circuit. The VCO core circuit includes a varactor that has a control node for receiving a control voltage. The control voltage generator circuit receives at least one proportional path (P-path) control input and an integral path (I-path) control input, and generates and outputs the control voltage to the control node of the varactor according to the at least one P-path control input and the I-path control input.