SAW Filter IDT Finger Layout for Ripple Suppression
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Solution Overview
Problem
Existing filters with slanted IDT electrode portions face issues with ripples near resonant and anti-resonant frequencies, which can degrade pass band characteristics in multiplexers and communication devices, especially when variant fingers are used uniformly, leading to interference between filter bands.
Innovation Solution
The use of a mixed arrangement of first and second electrode fingers in the IDT electrode of series resonators, where the first electrode fingers have a wider end portion and the second electrode fingers have a narrower end portion, is implemented to reduce or prevent ripples near both resonant and anti-resonant frequencies, thereby enhancing filter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a slanted IDT electrode portion is used to suppress transverse mode, then transverse mode is suppressed and Q factor is increased, but ripples appear near resonant frequency due to standing waves in gap portions
Solution Approach 1:
The patent applies local quality by making each electrode finger have a non-uniform width along its length, with a wider portion at one end and a narrower portion at the other end. This local variation in electrode finger width creates a gradient structure that suppresses standing waves in the gap portions between opposing electrode fingers, thereby reducing ripples near resonant frequency while maintaining the slanted IDT configuration for transverse mode suppression.
2Object-generated harmful factors
If uniform variant fingers are used in all resonators, then ripples near resonant frequency are reduced, but pass band characteristics of other filters are degraded due to interference from anti-resonant frequency ripples
Solution Approach 1:
The patent applies local quality by selectively configuring electrode fingers in different portions of the IDT electrode. Specifically, electrode fingers in different regions have different width profiles - with some having wider portions at specific ends and others having narrower portions. This localized differentiation in electrode finger design allows each resonator to suppress both resonant and anti-resonant frequency ripples, preventing interference with pass band characteristics of other filters in the multiplexer.
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 reduces or prevents ripples near resonant and anti-resonant frequencies, improving the pass band characteristics and insertion loss of filters, thus enhancing the performance of multiplexers and communication devices by minimizing interference between filter bands.
Implementation Method 1
an IDT electrode including a pair of comb-shaped electrodes on a substrate including a piezoelectric layer
Implementation Method 2
each of the pair of comb-shaped electrodes included in each of the one or more series resonators includes a plurality of electrode fingers extending in a direction orthogonal or substantially orthogonal to an acoustic wave propagation direction
Data Source
AI summary
A filter includes series resonators on a signal path, each of the series resonator including an IDT electrode that includes first electrode fingers each including a variant portion, second electrode fingers each including no variant portion, or both the first electrode fingers and the second electrode fingers, in the IDT electrode of one or more series resonators of the series resonators, a direction connecting other-side end portions of electrode fingers crosses an acoustic wave propagation direction, the IDT electrode includes the first electrode fingers, a first portion of an IDT electrode of another series resonator centrally located in the acoustic wave propagation direction, includes only the first electrode fingers, and a second portion and a third portion on two sides of the first portion each include only the second electrode fingers.