Voltage-Driven Series Resonant VCO for Low Phase Noise
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Solution Overview
Problem
Voltage controlled oscillators face limitations in reducing phase noise, especially in wireless communication systems, where strict requirements for minimizing communication errors are not met by existing solutions such as multi-core oscillators with parallel resonant circuits due to quality factor degradation and symmetry constraints.
Innovation Solution
A voltage controlled oscillator with a series resonant circuit coupled to an active voltage driving device, featuring a capacitive, inductive, and resistive component in series, which provides a higher series quality factor and reduces phase noise through a voltage-driven configuration, allowing for simpler circuit structure and reduced chip area without symmetry limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If inductors of the parallel resonant circuit are scaled down to reduce phase noise, then phase noise is reduced, but the quality factor Q is degraded
Solution Approach 1:
The patent inverts the conventional parallel resonant circuit configuration by using a series resonant circuit instead. This fundamental inversion allows the circuit to achieve both low phase noise and high quality factor simultaneously, as the series configuration naturally provides high Q factor while the voltage-driven operation minimizes phase noise without requiring small inductor values.
Solution Approach 2:
The patent changes the operational parameters by using a voltage-driven configuration rather than the conventional current-driven approach. This parameter change enables the series resonant circuit to operate at optimal points that simultaneously minimize phase noise and maintain high quality factor, avoiding the trade-off present in conventional designs.
2Object-affected harmful factors
If multi-core oscillators with parallel resonant circuits are used to reduce phase noise, then phase noise is reduced by 10 log(N), but the symmetric arrangement limits the number of cores that may be coupled together
Solution Approach 1:
The patent extracts the phase noise reduction benefit from the multi-core configuration by using a single series resonant circuit with voltage-driven operation. This eliminates the need for complex symmetric multi-core arrangements while achieving comparable or superior phase noise performance, thereby removing the symmetry constraints that limit scalability.
Solution Approach 2:
The patent segments the resonant circuit into distinct series-connected components (inductor, capacitor, resistor) that can be independently optimized. This segmentation allows for flexible design and implementation without requiring symmetric arrangements, enabling easier integration and scaling compared to multi-core parallel configurations.
3Object-affected harmful factors
If multi-core oscillators are used to reduce phase noise, then phase noise is reduced, but minor mismatches between oscillators significantly impair phase noise and penalize the figure of merit
Solution Approach 1:
The patent merges the functionality of multiple oscillators into a single series resonant circuit configuration. By combining the resonant elements and voltage-driven operation into one unified circuit, it eliminates the mismatch issues that arise from coupling multiple separate oscillators, while still achieving low phase noise performance.
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 voltage-driven series resonant circuit achieves significant phase noise reduction compared to dual current-driven parallel resonant circuits, enabling better performance in high-frequency applications and supporting advanced modulation schemes like QPSK and QAM with improved phase noise specifications.
Implementation Method 1
The series resonant circuit 2 is configured to resonate at a resonance frequency ω0 and has a series quality factor QS
Implementation Method 2
The active voltage driving device 3 is configured to provide a driving voltage Vx and to have a negative resistance in an operative voltage range VR
Data Source
Figure 1~3
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Figure 6~7
AI summary
A voltage controlled oscillator includes a series resonant circuit (2), having a resonance frequency (ω0) and an active voltage driving device (3), coupled to the series resonant circuit (2) and configured to provide a driving voltage (Vx) and to have an output negative resistance (R0) in an operative voltage range (VR) at the resonance frequency (ω0). The active voltage driving device (3) comprises a cross-coupled differential pair (20) having voltage supply terminals (3a, 3b) and the series resonant circuit (2) is coupled to the voltage supply terminals (3a, 3b) of the cross-coupled differential pair (20).