LiNbO3 Composite Filter Structure for Sezawa Wave Suppression
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Solution Overview
Problem
Existing bandpass filters utilizing Rayleigh waves in carrier aggregation systems suffer from adverse effects due to the appearance of Sezawa waves, which interfere with higher frequency bands, causing unwanted responses that affect filter performance.
Innovation Solution
A composite filter device is designed with an LiNbO3 substrate and IDT electrodes covered by a silicon oxide dielectric film, incorporating elastic wave resonators that utilize Rayleigh waves and feature an acoustic velocity of Sezawa waves equal to or higher than 4643.2 m/sec, including ladder filters and longitudinally coupled resonator filters to mitigate Sezawa wave interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a bandpass filter utilizing Rayleigh wave is used in carrier aggregation system, then the filter can operate in the designated frequency band, but a Sezawa wave (high-order mode) appears around frequency of approximately 1.2 times the Rayleigh wave frequency and causes unwanted responses that adversely affect higher frequency band filters
Solution Approach 1:
The patent converts the harmful Sezawa wave phenomenon into a beneficial filtering mechanism. By deliberately designing the filter to utilize the Sezawa wave's frequency characteristics (approximately 1.2 times the Rayleigh wave frequency), the unwanted high-order mode becomes a useful feature for suppressing signals in the frequency band between the first and second pass bands, thereby improving overall filter performance in carrier aggregation systems
Solution Approach 2:
The patent changes the acoustic velocity parameter of the Sezawa wave by modifying the filter structure. Specifically, it sets the acoustic velocity of the Sezawa wave to be equal to or higher than about 4643.2 m/sec through structural design adjustments, which shifts the Sezawa wave response frequency and prevents it from interfering with the higher frequency band pass filter operation
2Adaptability or versatility
If multiple bandpass filters with different frequency bands are connected to a common antenna terminal for carrier aggregation, then the system can support multiple carriers, but the Sezawa wave response from one filter adversely affects the performance of other filters in the same system
Solution Approach 1:
The patent converts the harmful inter-filter Sezawa wave interference into a beneficial shielding effect. The Sezawa wave response is positioned to create attenuation in the frequency band between the first and second pass bands, which naturally suppresses unwanted signals and protects the higher frequency band filter from adverse effects, thereby improving the reliability of the entire carrier aggregation system
Solution Approach 2:
The patent changes the acoustic velocity parameter to equal to or higher than about 4643.2 m/sec, which shifts the Sezawa wave frequency response away from the higher frequency band pass filter's operating range. This parameter adjustment ensures that multiple filters can coexist on a common antenna terminal without mutual interference, enabling reliable carrier aggregation operation
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
Effectively reduces or prevents the adverse effects of Sezawa waves on bandpass filters with higher frequency bands, enhancing the attenuation characteristics and reducing spurious responses, thereby improving filter performance in carrier aggregation systems.
Implementation Method 1
a Rayleigh wave propagating in the LiNbO3 substrate is utilized
Implementation Method 2
an elastic wave resonator which utilizes a Rayleigh wave propagating in the LiNbO3 substrate
Data Source
AI summary
A composite filter device for use in carrier aggregation includes a first bandpass filter connected to an antenna common terminal and including a first pass band, and a second bandpass filter including a second pass band of a higher frequency than the first pass band. The first bandpass filter includes an LiNbO3 substrate, an IDT electrode which is provided on the LiNbO3 substrate and defines the first bandpass filter, and a dielectric film which covers the IDT electrode and includes silicon oxide as a main component. The first bandpass filter is defined by at least one elastic wave resonator, and a Rayleigh wave propagating in the LiNbO3 substrate is used and an acoustic velocity of a Sezawa wave in the elastic wave resonator is equal to or higher than about 4643.2 m/sec.