Multiplexer Filter Layout for Suppressing Higher-Mode Spurious Emissions
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Solution Overview
Problem
Higher-mode spurious emissions in filters with elastic wave resonators can affect the characteristics of connected filters, leading to increased ripple in pass bands and insertion loss, particularly when the spurious emission frequency falls within another filter's pass band.
Innovation Solution
A multiplexer design with a first filter having two or more serial resonators and one or more parallel resonators, where the dielectric layer thickness of the resonators closest to the common terminal is reduced compared to the rest, to minimize higher-mode spurious emissions and insertion loss in connected filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dielectric layer is formed on the piezoelectric substrate to cover the IDT electrode in elastic wave resonators, then the filter can operate within its pass band, but higher-mode spurious emissions occur in the stop band which affect connected filters and increase ripple in their pass bands
Solution Approach 1:
The patent applies local quality by forming a first dielectric layer with a first thickness on the piezoelectric substrate at a first position, and a second dielectric layer with a second thickness (different from the first thickness) at a second position. This creates non-uniform local properties in the dielectric structure to suppress higher-mode spurious emissions while maintaining pass band characteristics. The different thicknesses at different positions allow selective control of resonance modes without compromising the overall filter performance.
2Ease of manufacture
If uniform dielectric layer thickness is used across all resonators, then manufacturing is simplified, but spurious emissions affect multiple filters in the multiplexer system
Solution Approach 1:
The patent implements local quality by creating dielectric layers with position-dependent thicknesses. The first dielectric layer has a first thickness at a first position and a second thickness at a second position, while the second dielectric layer similarly has varying thicknesses. This local variation in dielectric properties suppresses spurious emissions that would otherwise affect connected filters, while still being manufacturable through standard semiconductor fabrication processes that can control thickness variations.
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 higher-mode spurious emissions in the stop band of the first filter and minimizes insertion loss in the pass band of the second filter, improving resonance and transmission characteristics.
Implementation Method 1
Each of the plurality of elastic wave resonators includes a substrate having piezoelectricity, an IDT electrode including a pair of comb-shaped or substantially comb-shaped electrodes that are provided on the substrate
Implementation Method 2
there is a problem in that a higher-mode spurious emission is likely to occur in a frequency band (stop band) higher than its pass band
Data Source
AI summary
A first filter of a multiplexer includes serial resonators and parallel resonators that are acoustic wave resonators. A first of the serial resonators that is closer to a common terminal than the other serial resonators is connected to the common terminal without the parallel resonators interposed therebetween. Each of the elastic wave resonators includes a substrate having piezoelectricity, an IDT electrode provided on the substrate, and a dielectric layer provided on the substrate to cover the IDT electrode. A thickness of the dielectric layer of the first serial resonator is smaller than a thickness of each of the dielectric layers of the remainder of the elastic wave resonators.