Acoustic Wave Multiplexer IDT Layout for Stop Band Suppression
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Solution Overview
Problem
Multiplexers using acoustic wave resonators face issues with stop band responses affecting the characteristics of other filters, leading to increased ripple and insertion loss in the pass band, particularly when the stop band response frequency falls within the pass band of another filter.
Innovation Solution
The design incorporates a multiplexer structure with specific acoustic wave resonators, where the weight per unit area of the IDT electrode is increased for series and parallel resonators closest to the common terminal, reducing or preventing stop band responses and minimizing insertion loss in the pass band of adjacent filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If acoustic wave resonators with high acoustic wave energy confinement efficiency are used, then the filter achieves small size and small transmission loss, but a comparatively large stop band response is generated at the upper end of the stop band
Solution Approach 1:
The patent applies local quality by making the IDT electrode of specific resonators (those closest to the common terminal) have a larger weight per unit area than other resonators. This localized modification of electrode weight in critical positions suppresses stop band response generation at the upper end of the stop band while maintaining the high acoustic wave energy confinement efficiency and small transmission loss characteristics of the multilayer substrate structure.
2Adaptability or versatility
If the stop band response frequency is located inside the pass band of another filter, then the multiplexer can handle multiple frequency bands, but the stop band response causes an increase in ripple inside the pass band of the other filter
Solution Approach 1:
The patent makes the IDT electrode of resonators positioned to affect other filters (those closest to the common terminal) have a larger weight per unit area. This localized modification suppresses stop band response at frequencies that would otherwise fall within the pass band of other filters, thereby reducing pass band ripple while maintaining the multiplexer's capability to handle multiple frequency 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 approach effectively reduces or prevents stop band responses and minimizes insertion loss in the pass band of the second filter, enhancing the overall performance of the multiplexer by optimizing the weight per unit area of the IDT electrode in key resonators.
Implementation Method 1
acoustic wave resonators each include a substrate exhibiting piezoelectricity and an IDT electrode including a pair of comb-shaped electrodes provided on the substrate
Implementation Method 2
an acoustic wave device that is formed by stacking a high-acoustic-velocity film, a low-acoustic-velocity film, a piezoelectric film, and an IDT electrode in this order on a support substrate has been proposed... The acoustic wave device has high efficiency at confining acoustic wave energy in the thickness direction of a multilayer substrate
Implementation Method 3
acoustic wave resonators... can handle higher frequencies, and can realize a high Q value... A first series resonator that is closest to the common terminal among the two or more series resonators is electrically connected to the common terminal
Data Source
AI summary
A first filter of a multiplexer has a ladder filter structure including a plurality of series resonators and a plurality of parallel resonators. Each resonator is an acoustic wave resonator that includes an IDT electrode including a pair of comb-shaped electrodes. A portion having a unit area, in a plan view of a substrate on which the resonators are provided, has a larger weight in at least one of the IDT electrode of the series resonator that is closest to the common terminal, among the series resonator, and the IDT electrode of the parallel resonator that is closest to the common terminal than in the IDT electrode of each of the remainder of the plurality of acoustic wave resonators.