Acoustic Wave RF Filter IDT Modulation for Passband Stability
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Solution Overview
Problem
Existing acoustic wave RF filters in mobile devices face challenges in maintaining robustness against frequency response variations due to factors like process and temperature variations, which affect filter design specifications, particularly in next-generation mobile systems requiring tight band-to-band interference restrictions.
Innovation Solution
The method involves modulating the resonance frequency of Inter Digital Transducer (IDT) electrodes in acoustic wave filters by configuring them with non-periodic structures, dividing resonance frequencies into multiple sub-frequencies, and connecting resonators in parallel and series to optimize frequency response, thereby compensating for temperature and other variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional SAW resonators with periodic IDT structure are used, then the filter structure is simple and easy to manufacture, but the center-frequency varies significantly with temperature (about +/− 5 MHz from −30° C. to 85° C. in the 2 GHz range)
Solution Approach 1:
The patent applies parameter changes by modifying the IDT electrode structure from periodic to non-periodic, specifically by introducing different finger widths (first width for odd-numbered fingers, second width for even-numbered fingers) to achieve resonance frequency modulation. This structural parameter modification enables the filter to compensate for temperature-induced frequency shifts while maintaining manufacturing feasibility through standard photolithography processes.
2Reliability
If TC-SAW with additional processing steps is used, then the temperature compensation is improved (TCF reduced from about −40 ppm/° C. to about −20 ppm/° C.), but the manufacturing complexity increases
Solution Approach 1:
The patent extracts the temperature compensation function from additional processing layers (like SiO2 overlays in TC-SAW) and integrates it directly into the IDT electrode structure itself. By embedding the compensation mechanism within the existing IDT fingers through non-periodic width modulation, the solution eliminates the need for separate compensation layers or additional processing steps, thereby reducing device complexity while maintaining frequency stability.
3Manufacturing precision
If tighter band-to-band interference restrictions are imposed for next generation RF systems, then the filter selectivity is improved, but the design becomes more difficult and requires more complex filter structures
Solution Approach 1:
The patent applies local quality by creating non-uniform finger widths at specific locations within the IDT structure. The odd-numbered fingers have one width while even-numbered fingers have another width, creating localized variations in the electromagnetic field distribution. This local modification optimizes the frequency response and improves filter selectivity without requiring overall structural complexity or additional components.
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 approach enhances the filter's skirt characteristics, making it robust to frequency variations and ensuring compliance with design specifications across varying temperatures and other factors, thus improving filter performance.
Implementation Method 1
acoustic wave filter which is a band filter used in mobile communication devices that converts an electrical signal into an acoustic wave of a piezoelectric material using a piezoelectric effect of the piezoelectric material and converts the converted acoustic wave back into an electrical signal
Implementation Method 2
converts the converted acoustic wave back into an electrical signal
Data Source
AI summary
The present invention provides a method for design acoustic wave RF filter robust against variations of frequency response in passband by resonance frequency modulation of IDT enabling to improve the skirt characteristics in the passband of the filter by resonance frequency modulation with respect to the IDT electrodes of the resonators constituting the acoustic wave filter and determining the design parameters for the IDT electrodes based on the resonance frequency modulation so as to compensate for variations in frequency response due to effects of temperature variations as well as other factors.