Segmented VCO Resonators for Wide Tuning and Low Phase Noise
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Solution Overview
Problem
Voltage controlled oscillators face challenges in achieving low phase noise over a wide tuning range due to nonlinear modulation of varactor capacitance at low DC control voltages and reduced frequency tuning bandwidth caused by parasitic capacitances and inductances in varactor diode matrices.
Innovation Solution
A voltage controlled oscillator design featuring a plurality of series resonators with electrically variable capacitances and fixed inductors in a feedback arrangement with an active device, operating at a current density below the peak transition frequency, and segmented multi-transistor banks for improved thermal stability, which reduces high frequency voltage across varactors and increases tuning bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a low DC control voltage is used to cover a wide frequency bandwidth, then the frequency tuning range is improved, but the phase noise performance deteriorates due to significant and nonlinear varactor capacitance change
Solution Approach 1:
The invention divides the single resonator into multiple series resonators (typically 3-5), with each resonator containing varactor diodes. This segmentation distributes the high frequency voltage across multiple series elements, reducing the voltage stress on each individual varactor and minimizing nonlinear capacitance modulation, thereby improving phase noise performance while maintaining wide tuning range
Solution Approach 2:
The invention changes the operating parameters by using multiple series resonators with optimized L/C ratios and distributing the varactor capacitance changes across multiple elements. This parameter optimization ensures that each varactor operates in a more linear region, reducing phase noise while achieving wide frequency coverage
2Adaptability or versatility
If a varactor diode matrix is used to cover wide frequency bandwidth, then the frequency tuning range is improved, but the parasitic capacitances and inductances reduce the frequency tuning bandwidth
Solution Approach 1:
The invention segments the resonator structure into multiple series resonators, each with controlled parasitic elements. By distributing the varactor matrix across multiple resonators and using series configuration, the parasitic capacitances and inductances are minimized and their effects are reduced, allowing wider frequency tuning bandwidth
Solution Approach 2:
The invention optimizes the local quality of each resonator by carefully selecting L/C ratios and minimizing parasitic elements in each individual resonator. This local optimization ensures that each resonator contributes effectively to the overall frequency tuning range while minimizing the impact of parasitic impedances
3Speed
If high frequency voltage is applied across two varactor diodes, then the oscillator operates at the desired frequency, but the nonlinear modulation of varactor capacitance degrades phase noise
Solution Approach 1:
The invention divides the voltage stress across multiple series resonators, each containing varactor diodes. This segmentation reduces the high frequency voltage across each individual varactor, minimizing nonlinear capacitance modulation and improving phase noise performance while maintaining the desired oscillator frequency
Solution Approach 2:
The invention introduces fixed inductors and series resonator structures as intermediary elements between the varactor diodes and the high frequency signal. These intermediaries help distribute and control the voltage distribution, reducing nonlinear effects on the varactors and improving phase noise
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
This design results in improved, flatter phase noise performance and increased frequency tuning bandwidth by reducing nonlinear modulation and parasitic impedances, allowing the oscillator to operate effectively over a wider frequency range.
Implementation Method 1
a resonant circuit interconnected with the active circuit and including a plurality of series resonators each having an electrically variable capacitance and fixed inductor
Implementation Method 2
Two disadvantages of this voltage controlled oscillator are that a high frequency voltage applied to the resonator is applied across just two varactor diodes
Data Source
AI summary
A voltage controlled oscillator including an RF output terminal and a DC control terminal, an active circuit, and a resonant circuit interconnected with the active circuit and including a plurality of series resonators each having an electrically variable capacitance and fixed inductor; the active circuit includes at least one transistor having an operating current density which is approximately 35% or less of the peak fT operating current density and/or the active circuit includes a multi-transistor bank disposed in at least two separate sections, each pair of sections spaced apart to provide improved thermal uniformity among the transistors without substantially increasing parasitic impedance among them for providing an improved lower phase noise output at said RF output terminal.