Phononic Comb Quartz Oscillator Locking for Low Phase Noise

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Solution Overview

Problem

Existing quartz oscillators face challenges in achieving high stability, low phase noise, and reduced Size, Weight, and Power (SWaP) while maintaining g-sensitivity in the 10^-11 g range, especially in applications like radar, navigation, and communication.

Innovation Solution

The use of a phononic comb generated in a nonlinear quartz resonator to stabilize a second voltage-controlled crystal oscillator (VCXO) by locking it to a selected tooth of the comb, where the first derivative of the drive frequency versus the frequency of the selected tooth has an absolute value greater than 1, thereby reducing frequency instability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If nonlinear Duffing effects are used to improve phase noise in MEMS oscillators, then phase noise is reduced, but the system becomes highly sensitive to drive level changes and requires operation near the bifurcation point where frequency dependence on drive level is large

Engineering Contradiction:

Improvephase noiseVSAvoidfrequency insensitivity to drive amplitude

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent changes the operating parameters by driving the resonator below the strong nonlinear Duffing condition (prior to the onset of bifurcation), specifically operating at drive levels that produce less than roughly several hundred ppm drive-level induced shifts. This parameter change allows the system to achieve phase noise reduction while maintaining frequency insensitivity to drive amplitude variations

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a phononic comb as an intermediary structure that mediates between the drive signal and the output frequency. The comb teeth provide discrete frequency references that are less sensitive to drive level changes, acting as a buffer that decouples the phase noise reduction benefit from the drive level sensitivity problem

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If quartz oscillators are designed for high stability and low phase noise, then performance is improved, but Size, Weight, and Power (SWaP) increase

Engineering Contradiction:

ImprovestabilityVSAvoidSWaP

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The patent replaces traditional mechanical quartz oscillator designs with a phononic comb-based resonator system that uses acoustic wave phenomena. This substitution enables high stability performance while reducing the physical size and power consumption by utilizing the phononic bandgap structure to achieve high Q-factors in a compact MEMS implementation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If traditional VCXO designs are used, then size and power are kept small, but temperature stability and phase noise performance are insufficient

Engineering Contradiction:

Improvetemperature stabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The patent employs dynamic frequency tuning capabilities through the phononic comb structure, where the resonator can be electrically tuned to different frequencies while maintaining high stability. The voltage-controlled elements allow dynamic adjustment of the operating point on the phononic comb, enabling temperature compensation and phase noise reduction without proportionally increasing power consumption

Inventive Principle:

Principle #15Dynamics

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 approach enhances the stability of quartz oscillators by reducing phase noise and improving temperature stability with only a modest increase in size and power, while maintaining low g-sensitivity, thus addressing the limitations of existing technologies.

Implementation Method 1

Phononic combs form when one or more high-Q resonances are driven slightly off their resonant frequency into a nonlinear state

Methodology Applied

Scientific EffectPhononic comb generation: Resonance

Implementation Method 2

Nonlinear effects such as Duffing effects in MEMS resonators has been explored in the past to improve phase noise

Methodology Applied

Scientific EffectNonlinear Duffing effects:

Implementation Method 3

A plurality of piezoelectric resonators; first and second sustaining circuits coupled to first and second ones of the plurality of piezoelectric resonators

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentEP4035263B1Enhanced stability oscillators using a phononic comb

Publication Date: 2025.01.22 HRL LAB

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AI summary

A method and apparatus for enhancing the stability of an oscillator circuit by generating a comb of frequencies in a non-linear resonator member in response to a drive frequency, the oscillator circuit including a voltage controlled oscillator which is locked to a particular tooth of the comb of frequencies produced by the non-linear resonator member at a drive frequency for which the absolute value of the first derivative of the drive frequency versus said comb frequency is greater than 1, and wherein the second voltage controlled oscillator is coupled with a phase locked loop circuit which controls the locking of the second voltage controlled oscillator to said particular tooth of the comb of frequencies.