BAW Filter Resonator Polarity Layout for Harmonic Distortion Reduction

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Solution Overview

Problem

Bulk acoustic wave filters produce spurious output signals due to nonlinearities, leading to undesirable harmonic signals and intermodulation distortion, which are not effectively predicted or minimized by existing linear design models, particularly in high-power applications.

Innovation Solution

The implementation of a bulk acoustic wave filter circuit with series and shunt resonators, where the polarities of selected resonators are reversed to phase-shift and cancel harmonic signals, reducing overall nonlinear signal distortion and spurious output.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If high power input signals are provided to a BAW filter, then the filter can handle higher power applications, but the BAW filter produces a large amount of spurious output signals due to nonlinearities in the resonators

Engineering Contradiction:

Improveinput signal power handling capabilityVSAvoidspurious output signals

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The patent utilizes the nonlinear harmonic generation inherent in BAW resonators by deliberately configuring resonators with opposite polarities to generate equal but opposite phase harmonics. These harmful nonlinear effects are converted into a beneficial cancellation mechanism where the second harmonics from resonators with opposite polarities destructively interfere, reducing spurious output signals while maintaining high power handling capability

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent introduces asymmetry in the polarity configuration of BAW resonators within the filter circuit. By assigning opposite polarities to specific resonators and optimizing their distribution throughout the filter, the system creates an asymmetric structure that enables harmonic cancellation. This asymmetric configuration allows the filter to maintain its filtering function while reducing spurious signal generation at high power levels

Inventive Principle:

Principle #4Asymmetry

2Device complexity

If BAW filters are designed using only a linear model, then the design process is simplified, but spurious output signals cannot be predicted and minimized

Engineering Contradiction:

Improvedesign model complexityVSAvoidspurious signal prediction accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent changes the design approach by incorporating nonlinear parameters into the filter design process. Specifically, it uses a nonlinear model that accounts for the elastic coefficients, dielectric constants, and piezoelectric constants of the BAW resonators. This enables accurate prediction of spurious signal levels and allows optimization of resonator polarity configurations to minimize harmonic generation, while still maintaining practical design feasibility

Inventive Principle:

Principle #35Parameter changes

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 effectively minimizes undesirable harmonic signals and distortion, enhancing the filter's performance by partially canceling harmonics generated by the resonators, thereby improving the filter's ability to handle high-power input signals without generating unacceptable spurious outputs.

Implementation Method 1

bulk acoustic wave (BAW) resonators

Methodology Applied

Scientific EffectAcoustic wave: Sound

Implementation Method 2

resonant frequency

Methodology Applied

Scientific EffectResonance: Resonance

Implementation Method 3

nonlinear piezoelectric constants

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS7535323B2Bulk acoustic wave filter with reduced nonlinear signal distortion

Publication Date: 2009.05.19 CHEMTRON RESEARCH LLC

AI summary

A filter circuit includes at least one series resonator having a first terminal and a second terminal, where the first and second terminals of the at least one series resonator are coupled to an input and an output of the filter circuit, respectively. The filter circuit further includes at least one shunt resonator having a first terminal and a second terminal, where the first terminal of the at least one shunt resonator is coupled to the input of the filter circuit and the second terminal of the at least one shunt resonator is coupled to ground. A polarity of the first terminal of the at least one series resonator and a polarity of the first terminal of the at least one shunt resonator are selected so as to reduce harmonic signal generation and other types of distortion in the filter circuit.