Acoustic Wave Filter Multiplexer Using Intermediate-Pitch Resonators
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Solution Overview
Problem
Existing acoustic wave resonators with interdigital electrodes experience spurious responses at frequencies higher than the main mode due to bonding the piezoelectric layer to a support substrate, leading to reduced attenuation amounts and increased spurious responses.
Innovation Solution
A filter design incorporating series and parallel resonators with specific electrode finger pitches and an inductor connected to a resonator, where the inductor's inductance exceeds the maximum inductance of the parallel resonators, and the average pitch of the additional resonator is set to an intermediate value between the series and parallel resonators, compensating for spurious responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the piezoelectric layer is bonded to the support substrate, then the temperature-frequency coefficient is reduced, but spurious responses occur at frequencies higher than the main mode
Solution Approach 1:
The patent changes the pitch parameter of electrode fingers to suppress spurious responses. Specifically, it sets the pitch of series resonator electrode fingers to be different from the pitch of parallel resonator electrode fingers, and introduces an intermediate pitch value between the maximum first pitch and minimum second pitch to create attenuation poles that suppress spurious responses while maintaining the temperature compensation benefit of substrate bonding
Solution Approach 2:
The patent introduces an intermediate resonator with electrode fingers having an intermediate pitch as a mediator between the series and parallel resonators. This intermediate resonator creates attenuation poles at frequencies corresponding to spurious responses, thereby suppressing the harmful spurious signals while allowing the main mode to operate effectively
2Reliability
If parallel resonators are connected to ground with inductors, then the filter characteristics are improved, but spurious responses increase when inductance is insufficient
Solution Approach 1:
The patent optimizes the inductance parameter by setting it to be greater than the maximum inductance of inductors connected between parallel resonators and ground. This parameter change ensures that attenuation poles are properly formed to suppress spurious responses while maintaining good filter characteristics in the pass band
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
The design effectively suppresses spurious responses by adjusting electrode finger pitches and inductor inductance, enhancing attenuation amounts and maintaining the pass band characteristics.
Implementation Method 1
an acoustic wave resonator having a pair of interdigital electrodes on a piezoelectric layer
Implementation Method 2
an acoustic wave resonator having a pair of interdigital electrodes on a piezoelectric layer
Data Source
AI summary
A filter includes a support substrate, a piezoelectric layer, one or more series resonators connected in series between input and output terminals, each having first electrode fingers having a first average pitch, one or more parallel resonators having one end connected to a path and another end connected to a ground, each having second electrode fingers having a second average pitch more than a maximum first average pitch, another resonator having one end connected to the path, and having third electrode fingers having a third average pitch less than or equal to an intermediate value between the maximum first average pitch and a minimum second average pitch, and an inductor having one end connected to the another resonator and another end connected to the ground, and having an inductance more than a maximum inductance of another inductor connected between the parallel resonators and the ground.