Switched-Capacitor RF Resonator Tuning for Low Phase Noise

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Solution Overview

Problem

Active feedback RF resonators and oscillators suffer from phase noise that can be detrimental to circuit operation, particularly due to the sensitivity of varactor capacitance to bias voltage, limiting the tuning range and Q enhancement.

Innovation Solution

Incorporating a bank of switched fixed value capacitors with a tunable capacitor, such as a varactor, to reduce phase noise by adjusting the capacitance range and maintaining the tuning range, using the relationship ℒ(Δω) ≈ Q2(r2M)2⁢SVb(Δω) to optimize the number of switched capacitors M for desired phase noise reduction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a varactor is used for tuning the resonator, then the tuning range is extended, but the phase noise increases due to sensitivity to bias voltage

Engineering Contradiction:

Improvetuning rangeVSAvoidphase noise

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The capacitance tuning function is segmented into two parts: a switched capacitor bank providing coarse tuning steps and a varactor providing fine continuous tuning. This segmentation allows the system to achieve extended tuning range while maintaining low phase noise by operating the varactor at optimized bias points.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the operating parameters by introducing switched capacitors that provide discrete capacitance values, allowing the varactor to operate at optimized bias points that minimize phase noise while still achieving the desired tuning range through combination with the switched capacitor bank.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If the resonator Q is enhanced, then the frequency selectivity is improved, but the phase noise is amplified

Engineering Contradiction:

Improvefrequency selectivityVSAvoidphase noise

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The frequency tuning function is segmented between switched capacitors for coarse adjustment and varactor for fine adjustment, enabling Q enhancement through precise resonant frequency control while managing phase noise through optimized operating points.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The active feedback mechanism uses the segmented capacitance control to maintain stable oscillation at the desired frequency, enhancing Q while the switched capacitor/varactor combination minimizes phase noise by reducing sensitivity to bias voltage variations.

Inventive Principle:

Principle #23Feedback

3Object-affected harmful factors

If switched capacitors are added to reduce phase noise, then the device complexity increases

Engineering Contradiction:

Improvephase noiseVSAvoidcircuit complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The switched capacitor bank is merged with the varactor in a unified capacitance control architecture, where both components work together to provide tuning functionality. This integration achieves phase noise reduction without proportionally increasing complexity, as the components share common control logic and physical space.

Inventive Principle:

Principle #5Merging (Combining)

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

Phase noise is reduced by several orders of magnitude, allowing for extended tuning range and higher Q enhancement without sacrificing performance, applicable to both RF filters and oscillators.

Implementation Method 1

the sensitivity of varactor capacitance to bias voltage

Methodology Applied

Scientific EffectVaractor effect: Capacitance

Implementation Method 2

A BPF generally involves some form of resonator that stores energy in a given frequency band

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS12580544B2Phase noise reduction in a variable analogue RF resonator with switched capacitors

Publication Date: 2026.03.17 ANLOTEK LTD

AI summary

An active feedback RF resonator has a signal loop having a signal input and a signal output. The signal loop has a variable gain stage and at least one variable resonator, each variable resonator comprising an inductance element and a variable capacitance element comprising a number of switched fixed value capacitors and a variable capacitor. A phase noise of the active feedback RF signal has a maximum value for an operating frequency of the variable resonator that is based on an operating range of the variable capacitor.