Reactance Filter With Dual Piezoelectric Materials For Band 28
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Solution Overview
Problem
Current wireless communication technologies face challenges in defining frequency bands with large bandwidths and small band distances, particularly for band 28, due to limitations in surface acoustic wave filters, which struggle to meet both steep skirt attenuation and temperature coefficient requirements.
Innovation Solution
A reactance filter is designed using a ladder-type or lattice-type structure with series and parallel impedance elements, where first and second resonators are built on different piezoelectric materials, allowing independent optimization for steep skirts or large bandwidths, and utilizing separate substrates for each type of resonator to enhance coupling coefficients and reduce temperature coefficient effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a band pass filter is realized on lithium tantalate piezoelectric material to achieve small band distance and steep skirt, then the skirt steepness and band distance requirements are met, but the bandwidth requirement cannot be satisfied
Solution Approach 1:
The filter is divided into two separate sections: a first section using lithium tantalate resonators for achieving steep skirt and small band distance, and a second section using lithium niobate resonators for achieving large bandwidth. This segmentation allows each section to be optimized for its specific function without compromise.
Solution Approach 2:
The invention uses a composite structure combining two different piezoelectric materials (lithium tantalate and lithium niobate) in a single filter device. Each material is selected for its specific properties: lithium tantalate for steep skirt characteristics and lithium niobate for broad bandwidth, creating a composite filter that achieves both requirements simultaneously.
2Productivity
If a band pass filter is realized on lithium niobate piezoelectric material to achieve large bandwidth, then the bandwidth requirement is met, but the skirt steepness requirement is not satisfied
Solution Approach 1:
The filter is divided into two separate sections: a first section using lithium tantalate resonators for achieving steep skirt and small band distance, and a second section using lithium niobate resonators for achieving large bandwidth. This segmentation allows each section to be optimized for its specific function without compromise.
Solution Approach 2:
The invention uses a composite structure combining two different piezoelectric materials (lithium tantalate and lithium niobate) in a single filter device. Each material is selected for its specific properties: lithium tantalate for steep skirt characteristics and lithium niobate for broad bandwidth, creating a composite filter that achieves both requirements simultaneously.
3Reliability
If a filter is designed to comply with band definitions at each temperature, then temperature stability is achieved, but the complexity of meeting both bandwidth and band distance requirements increases
Solution Approach 1:
The invention changes the material parameter (piezoelectric material type) to achieve different temperature coefficients of frequency. By selecting materials with appropriate TCF values and combining them in specific configurations, the filter maintains compliance with band definitions across temperature variations while managing structural 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
The solution achieves a bandwidth of 6% and maintains a 10 MHz band distance, providing necessary attenuation in adjacent frequency bands while accommodating temperature variations, thus meeting the demanding specifications of band 28.
Implementation Method 1
Each of the parallel and series impedance elements comprises a resonator, a series circuit of such a resonator and a series inductance element, or a resonator and a capacitance element coupled in parallel. All resonators operate with acoustic waves.
Implementation Method 2
Document US 5 952 899 A relates to a ladder filter having edge reflection type SAW resonators. In detail, the document discloses a ladder filter including a plurality of series arm resonators and a plurality of parallel arm resonators. Each series arm resonator preferably includes an edge-reflection surface acoustic wave (SAW) resonator
Data Source
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AI summary
A reactance filter comprising first and second impedance elements arranged in a ladder-type structure is proposed where each impedance element comprises a resonator based on a piezoelectric material. Using different piezoelectric materials for first and second impedance elements provides a reactance filter having a large bandwidth and a passband with one sharp filter skirt.