Acoustic Wave Filter with Parallel Capacitors for Resonator Tuning
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Solution Overview
Problem
Existing acoustic wave devices used in ladder filters face challenges in separately adjusting the frequency of individual resonators, making it difficult to achieve precise frequency control.
Innovation Solution
A filter design incorporating a piezoelectric film made of lithium niobate or lithium tantalate, an acoustic wave resonator with a functional electrode, and a capacitor connected in parallel, allowing for easy adjustment of the resonator frequency by varying the thickness of the piezoelectric film and the capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the thickness of the piezoelectric substrate is adjusted to change frequency, then the frequency can be tuned, but it becomes difficult to separately adjust the frequency of individual resonators in a ladder filter
Solution Approach 1:
The patent divides the frequency control function into separate segments: the piezoelectric substrate thickness controls the base resonant frequency, while individual capacitors connected in parallel to each resonator enable separate frequency adjustment of each resonator. This segmentation allows independent control of each resonator's frequency without affecting others.
Solution Approach 2:
The patent changes the electrical parameter (capacitance) to achieve frequency adjustment. By connecting capacitors with different capacitance values in parallel to individual resonators, the resonant frequency of each resonator can be independently tuned without changing the physical dimensions of the piezoelectric substrate.
2Adaptability or versatility
If traditional acoustic wave devices are used in ladder filters, then they can function as filters, but the frequency of individual resonators cannot be easily adjusted
Solution Approach 1:
The patent introduces dynamic adjustability by connecting capacitors in parallel to each resonator. These capacitors can be varied to dynamically change the resonant frequency of individual resonators, transforming the static frequency characteristic into a dynamically adjustable one.
Solution Approach 2:
The capacitors are pre-connected in parallel to each resonator during device fabrication, establishing the frequency adjustment capability in advance. This preliminary configuration allows for easy frequency tuning during device operation or calibration without requiring complex external adjustment mechanisms.
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
Enables easy and precise adjustment of the frequency of individual resonators, facilitating improved performance and flexibility in ladder filter applications while also allowing for size reduction.
Implementation Method 1
an acoustic wave resonator that utilizes a bulk wave in a thickness slip mode propagating through a piezoelectric film
Implementation Method 2
a bulk wave in a thickness slip mode propagating through a piezoelectric film
Data Source
AI summary
A filter includes a piezoelectric film including lithium niobate or lithium tantalate, an acoustic wave resonator including a functional electrode on the piezoelectric film, a capacitor on the piezoelectric film and connected in parallel to the acoustic wave resonator, and a resonator electrically connected to the acoustic wave resonator. The functional electrode includes a pair of first and second electrodes facing each other in a direction intersecting a thickness direction of the piezoelectric film. When a thickness of the piezoelectric film is d and a center-to-center distance between the first electrode and the second electrode is p, d/p is smaller than or equal to about 0.5.