Acoustic Wave Filter Layout for Bragg Resonance Rejection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional acoustic wave filters face challenges in achieving high frequency-selectivity and sharp passband shapes while maintaining low insertion loss and compact size, especially in multifunctional devices with a crowded electromagnetic spectrum, where the Bragg resonance can distort the filter's high side passband and increase loss.
Innovation Solution
The design incorporates a piezoelectric layer with a monolithically disposed acoustic resonator structure and a lumped capacitive structure, where the interdigitated capacitive fingers and resonator fingers have specific orientations and undulations, and the capacitive structure is electrically coupled to the resonator structure, allowing for improved in-band and out-of-band rejection without increasing the filter's size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional acoustic wave filters are designed for high frequency-selectivity with sharp passband shapes, then the filter selectivity is improved, but the insertion loss increases and the size increases
Solution Approach 1:
The patent modifies the acoustic wave filter by adding a capacitive structure that changes the electrical parameters of the filter circuit. This capacitive coupling alters the impedance characteristics and resonant frequencies, enabling sharper frequency selectivity without the traditional penalty of increased insertion loss. The parameter change in the electrical configuration directly addresses the contradiction between selectivity and loss.
Solution Approach 2:
The invention combines the acoustic resonator structure with an additional capacitive structure to form a composite filtering system. This composite approach integrates two different functional elements (acoustic resonance and capacitive coupling) to achieve performance characteristics that neither element could provide alone, specifically improving frequency selectivity while maintaining low insertion loss.
2Measurement precision
If conventional acoustic wave filters are designed for high frequency-selectivity with sharp passband shapes, then the filter selectivity is improved, but the filter size increases
Solution Approach 1:
By changing the electrical parameters through capacitive coupling, the filter achieves sharp frequency selectivity without requiring physical expansion of the resonator structure. The parameter modification in the electrical domain allows compact geometric dimensions to maintain high selectivity performance.
Solution Approach 2:
The capacitive structure serves multiple functions simultaneously: it provides frequency selectivity enhancement, maintains impedance matching, and occupies minimal space. This multi-functionality allows the filter to achieve high frequency-selectivity without proportional increases in physical size.
3Measurement precision
If the Bragg resonance is present in conventional acoustic wave filters, then the resonant frequency response is achieved, but the high side passband is distorted and loss increases
Solution Approach 1:
The patent converts the harmful effect of Bragg resonance (which causes passband distortion) into a beneficial feature. By introducing capacitive coupling, the system utilizes the Bragg resonance phenomenon to create additional useful transmission zeros that enhance frequency selectivity. The harmful distortion is transformed into a mechanism for improving out-of-band rejection and defining sharper passband edges.
Solution Approach 2:
The capacitive structure acts as an intermediary element that mediates between the acoustic resonator and the external circuit. It modifies the interaction between the acoustic wave and the electrical circuit, controlling how Bragg resonance manifests in the frequency response. This intermediary function allows the system to achieve the desired resonant frequency response while eliminating the harmful passband distortion.
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 enhances the rejection on both sides of the passband, narrows the filter's bandwidth, and moves the Bragg resonance further from the passband, resulting in steeper filter skirts and improved out-of-band rejection, suitable for applications in telecommunications systems.
Implementation Method 1
an acoustic resonator structure monolithically disposed on the piezoelectric layer
Implementation Method 2
resonators, which store energy very efficiently at a resonant frequency
Implementation Method 3
a lumped capacitive structure monolithically disposed on the piezoelectric layer and being electrically coupled to the acoustic resonator structure
Data Source
AI summary
An acoustic filter comprises a piezoelectric layer; an acoustic resonator structure monolithically disposed on the piezoelectric layer, the acoustic resonator structure including an arrangement of planar interdigitated resonator fingers; and a lumped capacitive structure monolithically disposed on the piezoelectric layer and being electrically coupled to the acoustic resonator structure, the lumped capacitive structure including an arrangement of planar interdigitated capacitive fingers, each of at least one of the interdigitated capacitive fingers having an edge that is entirely continuous.