IDT Electrode Finger Segmentation for RF Filter Ripple Reduction
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Solution Overview
Problem
Conventional filters with inclined IDT electrode portions effectively reduce transverse mode ripples near resonant frequencies but introduce ripples near anti-resonant frequencies, which can degrade pass band characteristics in multiplexers, especially when variant fingers cause interference across different filter bands.
Innovation Solution
The design incorporates a pair of input and output terminals connected by series resonators with IDT electrodes featuring comb-teeth electrodes, where first and second electrode fingers with varying widths are arranged in a specific order to intersect the acoustic wave propagation direction, reducing ripples at both resonant and anti-resonant frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an inclined IDT electrode portion is used to suppress transverse mode, then a ripple in the vicinity of the resonant frequency is reduced, but a ripple in the vicinity of the anti-resonant frequency is caused
Solution Approach 1:
The IDT electrode is segmented into multiple electrode fingers with different widths. Specifically, the electrode fingers are divided into a first plurality with a first width and a second plurality with a second width different from the first width. This segmentation allows different portions of the electrode to contribute differently to the acoustic wave generation, enabling suppression of both resonant and anti-resonant ripples simultaneously.
Solution Approach 2:
Different regions of the IDT electrode are assigned different local properties through varying electrode finger widths. The first plurality of electrode fingers has a first width optimized for suppressing resonant frequency ripple, while the second plurality has a second width optimized for suppressing anti-resonant frequency ripple. This local quality variation resolves the contradiction by allowing each region to address specific frequency-related issues.
2Manufacturing precision
If variant fingers are used to reduce ripple near resonant frequency, then resonant frequency characteristic is improved, but ripple near anti-resonant frequency increases affecting pass band of different filters
Solution Approach 1:
The electrode fingers are segmented into two distinct groups with different widths. The first plurality of electrode fingers addresses the resonant frequency characteristic, while the second plurality addresses the anti-resonant frequency ripple that affects other filter pass bands. This segmentation enables independent optimization of each frequency characteristic without compromising the other.
Solution Approach 2:
The electrode finger width parameter is changed across different portions of the IDT electrode. By varying the width parameter between the first and second plurities of electrode fingers, the patent achieves different acoustic coupling characteristics that respectively address resonant and anti-resonant frequency issues, thereby improving overall filter performance across multiple bands.
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 effectively minimizes ripples near both resonant and anti-resonant frequencies, enhancing the pass band characteristics and insertion loss of filters, thereby improving the performance of multiplexers and radio frequency front-end circuits.
Implementation Method 1
an IDT electrode including a pair of comb-teeth electrodes on a substrate including a piezoelectric layer
Implementation Method 2
one or more series resonators along a signal path connecting the input and output terminals
Data Source
AI summary
A filter includes series resonators in a signal path. An IDT electrode included in the series resonators includes at least either first electrode fingers including variant portions or second electrode fingers not including variant portions. In the IDT electrode included in one or more series resonators of the series resonators, a direction that connects the respective other ends of a plurality of electrode fingers intersects an acoustic wave propagation direction. In a first portion and a second portion of the IDT electrode, the first and second electrode fingers are arranged in a predetermined order.