Apodized SAW Resonator Layout for Spurious Response Suppression

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Solution Overview

Problem

Conventional surface acoustic wave resonators with LiNbO3 substrates suffer from spurious responses due to resonance in the transverse mode, especially when the number of comb electrode fingers is increased, which degrades in-band frequency characteristics and capacitance, making it difficult to achieve wide frequency band filters with suppressed spurious responses.

Innovation Solution

The use of two surface acoustic wave resonators with apodized comb electrodes, each having a smaller number of fingers, connected in parallel on a piezoelectric substrate, effectively suppresses undesired resonance in the transverse mode and provides a desired electrostatic capacitance, even with a large number of comb electrode fingers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the number of comb electrode fingers is increased to achieve wide frequency band filtering, then the frequency band is widened, but spurious responses due to resonance in the transverse mode occur and in-band frequency characteristics are degraded

Engineering Contradiction:

Improvefrequency band widthVSAvoidspurious responses

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The patent divides a single comb electrode structure with many fingers into multiple separate comb electrode structures with fewer fingers each. By segmenting the electrode system, the transverse mode resonance problem is avoided while maintaining the overall capacitance needed for wide frequency band operation. The multiple segmented electrodes are arranged and connected to collectively provide the required electrical characteristics without generating spurious responses.

Inventive Principle:

Principle #1Segmentation

2Quantity of substance

If the number of comb electrode fingers is increased to increase capacitance, then the capacitance is increased, but spurious responses occur due to resonance in the transverse mode

Engineering Contradiction:

Improveelectrostatic capacitanceVSAvoidspurious responses

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

The patent segments the electrode system into multiple comb electrode structures, each with a manageable number of fingers that avoids transverse mode resonance. The total capacitance is achieved by combining multiple segmented electrodes with appropriate geometries and arrangements, rather than using a single large electrode structure that would generate spurious responses.

Inventive Principle:

Principle #1Segmentation

3Adaptability or versatility

If LiNbO3 substrates are used to widen frequency bands due to large electromechanical coupling coefficient, then the frequency band is widened, but in-band frequency characteristics are degraded due to spurious responses

Engineering Contradiction:

Improvefrequency band widthVSAvoidin-band frequency characteristics

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent employs segmented comb electrodes on LiNbO3 substrates to maintain the advantage of wide frequency band operation while eliminating the disadvantage of spurious responses. The segmentation approach allows the use of high electromechanical coupling coefficient materials without suffering from transverse mode resonance problems.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies different overlapping lengths to different segments of the comb electrodes, creating local variations in the electrode structure. This local quality differentiation allows each segment to be optimized independently, suppressing spurious responses while maintaining overall wide band characteristics.

Inventive Principle:

Principle #3Local quality

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 configuration achieves a surface acoustic wave resonator with suppressed spurious responses and desired capacitance, enabling wide frequency band filtering with improved temperature characteristics and reduced insertion loss, enhancing the flexibility in designing ladder type filters.

Implementation Method 1

surface acoustic wave resonator having comb electrodes with different overlapping lengths... piezoelectric substrate... surface acoustic wave resonators

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

comb electrodes... electrostatic capacitance... resonance in the transverse mode

Methodology Applied

Scientific EffectElectrostatic force: Electrostatics

Data Source

PatentUS8084915B2Surface acoustic wave resonator having comb electrodes with different overlapping lengths

Publication Date: 2011.12.27 SKYWORKS PANASONIC FILTER SOLUTIONS JAPAN

AI summary

A surface acoustic wave resonator includes a piezoelectric substrate, a first surface acoustic wave resonator having a comb electrode provided on the piezoelectric substrate, and a second surface acoustic wave resonator having a comb electrode provided on the piezoelectric substrate. The first surface acoustic wave resonator and the second surface acoustic wave resonator are apodized and connected in parallel.