SAW Multiplexer Electrode Layout for Wider RF Passband
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Solution Overview
Problem
Existing multiplexers using surface acoustic wave (SAW) filters face challenges in maintaining a wide bandwidth due to stopband ripples and insertion loss issues, particularly on the higher frequency side, which affect the transmission characteristics of radio-frequency (RF) signals.
Innovation Solution
The design incorporates a multiplexer configuration with apodization-weighting IDT electrodes and variant finger structures in SAW resonators, including a higher ratio of fourth electrode fingers closest to the common connection terminal, and slanted IDTs to reduce transverse mode ripples and maintain high Q values, thereby preventing bandwidth narrowing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the resonant frequency of the parallel arm resonator closest to the common connection terminal is made lower than other parallel arm resonators to provide impedance nearer to short side, then the impedance matching is improved, but stopband ripples are generated at higher frequency end within the passband and the bandwidth of the passband becomes narrower
Solution Approach 1:
The patent applies local quality by making the IDT electrode of the parallel arm resonator closest to the common connection terminal have a different electrode finger width compared to other parallel arm resonators. Specifically, the first IDT electrode has electrode fingers with a width that provides impedance closer to the short side, while other IDT electrodes have different electrode finger widths. This localized differentiation allows each resonator to contribute optimally to impedance matching without generating stopband ripples that narrow the passband bandwidth.
2Reliability
If the capacitance of the parallel arm resonator closest to the common connection terminal is made greater than other parallel arm resonators to provide impedance nearer to short side, then the impedance matching is improved, but the bandwidth of the passband becomes narrower due to stopband ripples
Solution Approach 1:
The patent employs parameter changes by adjusting the electrode finger width of the IDT electrode in the parallel arm resonator closest to the common connection terminal. By changing this geometric parameter, the capacitance of this specific resonator is optimized to provide impedance nearer to the short side for better matching, while the electrode finger width is carefully controlled to prevent stopband ripples from entering the passband, thus maintaining wide bandwidth.
3Device complexity
If conventional IDT electrodes are used in SAW resonators, then the device complexity is reduced, but transverse mode ripples occur and Q values decrease
Solution Approach 1:
The patent applies local quality by implementing slanted IDT electrodes where the electrode fingers are oriented at an angle rather than perpendicular to the propagation direction. This localized structural modification in the IDT electrode design suppresses transverse mode ripples and maintains high Q values while adding only moderate complexity to the device structure.
Solution Approach 2:
The patent employs asymmetry by designing IDT electrodes with non-uniform electrode finger widths, where the first IDT electrode has a different electrode finger width compared to other IDT electrodes in the same resonator. This asymmetric design optimizes the electrical characteristics and Q value of the SAW resonator while managing the device complexity.
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 significantly reduces stopband ripples and insertion loss, broadening the passband bandwidth and improving the tolerance to temperature and processing variations, enhancing the yield rate and reducing insertion loss in RF front-end circuits and communication apparatuses.
Implementation Method 1
an IDT electrode and a reflector provided on a substrate, and the IDT electrode includes a pair of comb-shaped electrodes
Implementation Method 2
a multiplexer that isolates a radio-frequency (RF) signal with a plurality of wireless carrier frequencies is arranged immediately after an antenna of a communication apparatus. As a plurality of bandpass filters included in the multiplexer, elastic wave filters having low loss in their passbands
Data Source
AI summary
A multiplexer includes a first reception-side filter and a second reception-side filter whose passband has frequencies higher than the first reception-side filter. The first reception-side filter includes a series arm resonator provided on a first path, and parallel arm resonators provided on a path electrically connecting the first path and ground. A direction connecting tips of a plurality of electrode fingers included in each resonator crosses an elastic wave propagating direction at a certain angle. The parallel arm resonator closest to a common connection terminal does not include third electrode fingers, and the other parallel arm resonators include third electrode fingers.