SAW Filter IDT Layout for Right-Side Band Attenuation
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Solution Overview
Problem
Surface acoustic wave filters face challenges in achieving improved attenuation characteristics, particularly on the right side of the transmission band, due to limitations in adjusting the period of interdigital transducer (IDT) electrodes and electromechanical coupling coefficients.
Innovation Solution
The design incorporates a surface acoustic wave filter with a series of resonators and capacitors, where the period of IDT electrodes decreases towards the ends of the bus bars, and capacitors are connected in parallel to specific resonators to reduce the electromechanical coupling coefficient, enhancing right-side attenuation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the period of IDT electrodes is adjusted to improve right-side attenuation characteristics, then the attenuation performance is improved, but the filter design complexity increases
Solution Approach 1:
The patent applies local quality by varying the period of IDT electrodes in specific regions (first and third areas) while maintaining a reference period in the central region (second area). This localized modification of electrode period creates additional resonance/anti-resonance phenomena that improve right-side attenuation characteristics without requiring complete redesign of the entire filter structure.
Solution Approach 2:
The filter structure is segmented into distinct regions (first area, second area, third area) with different electrode period characteristics. This segmentation allows independent optimization of different parts of the filter, enabling improved attenuation performance through controlled variation in specific zones while maintaining overall structural integrity.
2Reliability
If capacitors are connected in parallel to resonators to reduce electromechanical coupling coefficient, then right-side attenuation is improved, but the device complexity increases
Solution Approach 1:
Capacitors are introduced as intermediary elements connected in parallel to specific series resonators. These capacitors act as mediators that reduce the electromechanical coupling coefficient of the resonators, thereby improving right-side attenuation characteristics. The capacitors provide a controlled mechanism to adjust coupling without fundamentally changing the resonator structure.
3Reliability
If the period of IDT electrodes decreases towards the ends of bus bars, then additional resonance phenomena are generated to improve attenuation, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements parameter changes by systematically varying the period parameter of IDT electrodes across different regions. The period transitions from a reference period in the central area to progressively smaller periods in the first and third areas. This controlled parameter variation generates additional resonance phenomena that enhance attenuation while providing a clear design specification for manufacturing.
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 improves the attenuation and sensitivity characteristics on the right side of the transmission band by generating additional resonance/anti-resonance phenomena and reducing the electromechanical coupling coefficient, resulting in enhanced filter performance.
Implementation Method 1
A surface acoustic wave element is an electro-mechanical device which utilize the interaction between the surface acoustic waves and semiconductor conductive electrons, and uses the surface acoustic waves transferred onto the surface of piezoelectric crystals.
Implementation Method 2
A surface acoustic wave (SAW) refers to a wave propagating along the surface of an elastic solid. Such a surface acoustic wave concentrates and propagates energy close to the surface, and corresponds to a mechanical wave.
Implementation Method 3
at least one of the plurality of series resonators includes: first and second bus bars, which extend parallel to each other in a first direction within first to third areas sequentially arranged on a substrate; a plurality of first interdigital (IDT) transducer electrodes which extend in a second direction perpendicular to the first direction from the first bus bar
Data Source
AI summary
Provided is a surface acoustic wave filter with improved attenuation characteristics. The surface acoustic wave filter includes: a plurality of series resonators which are connected between an input terminal and an output terminal; and at least one parallel resonator which connects between a ground terminal and two adjacent series resonators among the plurality of series resonators, wherein at least one of the plurality of series resonators includes: first and second bus bars, which extend parallel to each other in a first direction within first to third areas sequentially arranged on a substrate; a plurality of first interdigital (IDT) transducer electrodes which extend in a second direction perpendicular to the first direction from the first bus bar; and a plurality of second IDT electrodes which extend in the second direction from the second bus bar and are alternately arranged with the plurality of first IDT electrodes, wherein the plurality of first IDT electrodes and the plurality of second IDT electrodes are alternately arranged with a reference period in the second area, are alternately arranged in the first area with a period which gets smaller than a reference period in the direction of one end of the first bus bar, and are alternately arranged in the third area with a period which gets smaller than a reference period in the direction of the other end of the first bus bar.