Acoustic Wave Filter Pitch Variation for Spurious Mode Suppression
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Solution Overview
Problem
Acoustic wave filters with longitudinally coupled resonators suffer from deficient attenuation characteristics due to spurious acoustic wave excitation, leading to degraded isolation in multiplexers, primarily because the electrode finger pitch variations are too regular, resulting in insufficient acoustic impedance mismatch.
Innovation Solution
The acoustic wave filter design incorporates a longitudinally coupled resonator with IDT electrodes and reflectors where the standard deviation of the pitch deviation rate of the electrode finger pitch is greater than or equal to 1.4%, introducing irregular variations to prevent spurious wave excitation and enhance attenuation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If electrode finger pitch varies regularly in secondary excitation regions, then low-loss performance is achieved, but spurious acoustic waves are excited causing deficient attenuation characteristics
Solution Approach 1:
The patent applies asymmetry by making the pitch variation irregular rather than regular. The pitch deviation rate is designed to have a standard deviation of at least 1.4%, creating an asymmetric and non-periodic pitch pattern that prevents spurious wave excitation while maintaining the low-loss performance achieved through pitch variation.
Solution Approach 2:
The patent changes the parameter of pitch deviation rate distribution by specifying that its standard deviation must be at least 1.4%. This parameter change transforms the regular pitch variation into irregular pitch variation, effectively suppressing spurious acoustic waves while preserving the beneficial low-loss characteristics.
2Object-generated harmful factors
If electrode finger pitch varies regularly to achieve low-loss performance, then attenuation characteristics degrade, but isolation characteristics in multiplexers are improved
Solution Approach 1:
The patent uses asymmetry by designing irregular pitch variation with a standard deviation of pitch deviation rate of at least 1.4%. This irregular pattern simultaneously improves attenuation characteristics by suppressing spurious waves and enhances isolation characteristics in multiplexers, resolving the contradiction between these two performance aspects.
Solution Approach 2:
The patent specifies a minimum standard deviation of 1.4% for the pitch deviation rate, which transforms regular pitch variation into irregular pitch variation. This parameter change achieves both improved attenuation characteristics and enhanced isolation characteristics, resolving the contradiction between these two performance metrics.
3Object-generated harmful factors
If pitch variation is introduced to improve attenuation characteristics, then spurious wave excitation occurs, but acoustic impedance mismatch is insufficient
Solution Approach 1:
The patent optimizes the pitch deviation rate standard deviation to be at least 1.4%, which provides sufficient acoustic impedance mismatch to suppress spurious wave excitation and improve attenuation characteristics. This precise parameter control resolves the contradiction between achieving adequate impedance mismatch and maintaining manufacturing feasibility.
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 significantly improves the attenuation characteristics of the acoustic wave filter and the isolation in multiplexers by reducing spurious acoustic wave excitation and ensuring efficient signal propagation, as evidenced by increased isolation in the transmission band.
Implementation Method 1
The longitudinally coupled resonator includes a piezoelectric substrate, a plurality of interdigital transducer (IDT) electrodes, and a reflector
Implementation Method 2
the standard deviation of the deviation rate of at least one of the reflector and the plurality of IDT electrodes is greater than or equal to about 1.4%, wherein a k-th electrode finger pitch is a distance between a k-th electrode finger and a (k+1)th electrode finger
Data Source
AI summary
An acoustic wave filter includes a longitudinally coupled resonator including IDT electrodes and a reflector. A standard deviation of a pitch deviation rate of at least one of the reflector and the IDT electrodes is greater than or equal to about 1.4%.