Acoustic Wave Filter Wiring Layout for Steep Low-Loss Passbands
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Solution Overview
Problem
Existing frequency variable type acoustic wave devices face challenges in maintaining steepness and low loss characteristics of the pass band, particularly on the low-band side, due to limitations in the configuration of capacitance elements and acoustic wave resonators.
Innovation Solution
The proposed acoustic wave device incorporates a configuration with a first and second resonance circuit, featuring a first acoustic wave resonator with an interdigital transducer (IDT) electrode and a frequency variable circuit, including a capacitance element and a switch, where the second capacitance element is formed by intersecting IDT and capacitance wirings on the same substrate, allowing for adjustable film thicknesses and high Q values, thereby enhancing the bandpass characteristic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a comb-tooth electrode is used as the capacitance element to enhance the steepness of the pass band on the low-band side, then the steepness is improved, but the low loss characteristic in the pass band deteriorates due to low Q value
Solution Approach 1:
The capacitance element is segmented into multiple capacitors connected in series, where at least one capacitor has a capacitance value different from the others. This segmentation allows optimization of the Q value while maintaining the desired capacitance for steepness, resolving the contradiction between steepness and low loss characteristic.
Solution Approach 2:
Different capacitors in the series connection have different capacitance values, creating local quality variations. This allows specific capacitors to be optimized for high Q value (low loss) while others contribute to the overall capacitance needed for steepness, thereby resolving the technical contradiction.
2Reliability
If the film thickness of the IDT electrode is increased to improve the Q value of the capacitance element, then the low loss characteristic is improved, but the manufacturing complexity and cost increase
Solution Approach 1:
Instead of changing the film thickness parameter of the IDT electrode, the invention changes the capacitance values of the capacitors in the series connection. This parameter substitution allows achieving the desired Q value without the complexity and cost of precise film thickness control.
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 secures the steepness and low loss characteristic of the pass band on the low-band side, improving the bandpass characteristic of the acoustic wave device by allowing for larger capacitance Q values and adjustable capacitance values without increasing the film thickness of the IDT electrode.
Implementation Method 1
a first acoustic wave resonator including a first interdigital transducer (IDT) electrode
Data Source
AI summary
A variable filter (10) includes a parallel arm resonance circuit and a serial arm resonance circuit, the parallel arm resonance circuit includes a parallel arm resonator (p1) having an IDT electrode (121) and a frequency variable circuit (11) connected to the parallel arm resonator (p1), the frequency variable circuit (11) includes a capacitance element (C1) and a switch (SW), the variable filter (10) further includes a capacitance element (C2) connected between a serial arm and ground, the IDT electrode (121), an IDT wiring connected to the IDT electrode (121), and a capacitance wiring connected to the capacitance element (C1) are formed on the same substrate, a wiring (141 or 144) of the capacitance wirings and a wiring (143) of the IDT wirings intersect with each other, and the capacitance element (C2) is configured of the capacitance wiring and the IDT wiring in the intersection region.