Surface Acoustic Wave Resonator With Variable IDT Pitch for Wide Passbands
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Solution Overview
Problem
Conventional surface acoustic wave filters face challenges in achieving wide pass bands with low insertion loss and improved flatness, as the resonance mode generated by a narrow electrode finger pitch at the end of IDT electrodes is not sufficiently adjustable, leading to inadequate antenna gain and increased power consumption in mobile communications equipment.
Innovation Solution
A surface acoustic wave resonator with a configuration of variable and fixed pitch sections for IDT electrodes, where the electrode finger pitch decreases towards the boundary between adjacent electrodes, allowing for fine adjustment of frequency spacing and mode conversion, thereby preventing radiation loss and optimizing resonance peak placement for wide band characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the distance between adjacent IDT electrodes is shortened or a narrow pitch section is provided at the end of the IDT electrode, then the pass band can be widened, but the resonance mode cannot be sufficiently adjusted and the insertion loss and flatness cannot be further improved
Solution Approach 1:
The patent applies local quality by dividing the IDT electrode into sections with different electrode finger pitches. Specifically, a first IDT electrode has a first electrode finger pitch in its first section and a second electrode finger pitch (different from the first) in its second section. This allows different regions of the same electrode to have different local characteristics, enabling both wide pass band and adjustable resonance mode simultaneously.
2Area of moving object
If a narrow pitch section is provided at the end of the IDT electrode, then the pass band can be widened, but the insertion loss and flatness of the filter cannot be further sufficiently improved
Solution Approach 1:
The patent uses local quality by creating sections with different electrode finger pitches within the same IDT electrode. The first section has a first pitch optimized for certain characteristics, while the second section has a second pitch optimized for other characteristics. This local differentiation allows the filter to achieve both wide pass band and low insertion loss with improved flatness.
Solution Approach 2:
The patent applies dynamics by making the electrode finger pitch variable along the length of the IDT electrode. Instead of a uniform static pitch, the pitch changes from the first value to the second value across different sections, creating a dynamic structure that can optimize multiple performance parameters simultaneously including insertion loss and pass band characteristics.
3Area of moving object
If the distance between adjacent IDT electrodes is shortened, then the pass band can be widened, but the resonance mode generated cannot be most suitably arranged
Solution Approach 1:
The patent applies local quality by creating sections with different electrode finger pitches. The first section with the first pitch generates certain resonance modes, while the second section with the different pitch generates different resonance modes. This allows precise control and arrangement of resonance modes while maintaining a wide pass band, resolving the contradiction between pass band width and resonance mode arrangement precision.
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 enables the realization of a surface acoustic wave apparatus with a wide pass band, low insertion loss, and improved electrical characteristics, effectively addressing the limitations of conventional filters by allowing for better control of filter characteristics and reduced power consumption.
Implementation Method 1
An IDT electrode 204 having a plurality of electrode fingers arranged on a piezoelectric substrate 202 comprises a pair of comb-shaped electrodes in a state where they are opposed to each other and meshed with each other. An electric field is applied to the pair of comb-shaped electrodes, to generate a surface acoustic wave.
Implementation Method 2
the excited surface acoustic wave propagates to IDT electrodes 203 and 205 arranged on both sides of the IDT electrode 204. The surface acoustic wave is reflected by the reflector electrodes 210, 211, 212, and 213 positioned at both ends, and is changed into standing waves between the reflector electrodes at both the ends.
Implementation Method 3
the electrode finger pitch in the variable pitch section basically decreases toward the boundary between the two adjacent IDT electrodes, and the minimum electrode finger pitch portion in the two adjacent variable pitch sections is on one side spaced apart from the boundary
Data Source
AI summary
A plurality of IDT electrodes 2 to 7 each having a large number of electrode fingers extending in a direction perpendicular to a propagation direction of a surface acoustic wave propagating on a piezoelectric substrate 1 are arranged on the piezoelectric substrate 1 along the propagation direction, and each of the two adjacent IDT electrodes out of the plurality of IDT electrodes 2 to 7 comprises a variable pitch section and a fixed pitch section. The electrode finger pitch in the variable pitch section gradually decreases toward the boundary between the two adjacent IDT electrodes, and the minimum electrode finger pitch portion in the two variable pitch sections is on one side spaced apart from the boundary. There can be provided a surface acoustic wave apparatus having a large pass bandwidth, having a low insertion loss, and having improved flatness in a pass band.