Narrow-Aperture SAW Resonators for Steeper Filter Skirts
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Solution Overview
Problem
Designing acoustic wave filters with a steep filter skirt is challenging, particularly for surface acoustic wave (SAW) filters, as they often struggle to meet steepness specifications near the passband without additional circuit components or piston mode structures, which can complicate the design and increase insertion loss.
Innovation Solution
The implementation of acoustic wave filters with a transverse spurious mode is achieved by using series and shunt resonators with specific interdigital transducer electrode apertures, concentrating the transverse spurious mode at a frequency to enhance the steepness of the filter skirt without external components, and employing temperature-compensated surface acoustic wave resonators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional SAW filter designs are used, then the filter structure is simple, but the filter skirt steepness is insufficient and insertion loss increases
Solution Approach 1:
The patent changes the physical parameters of the IDT electrode by reducing its aperture to less than 10 wavelengths (preferably less than 7 wavelengths). This parameter change concentrates the transverse spurious mode at a specific frequency, which increases the filter skirt steepness and improves rejection of frequencies close to the passband while maintaining acceptable insertion loss characteristics
Solution Approach 2:
The patent converts the harmful transverse spurious mode into a beneficial feature. Instead of suppressing the transverse mode as in conventional designs, the narrow aperture IDT is designed to concentrate the transverse spurious mode at a frequency that enhances filter skirt steepness, thereby improving filter performance without requiring additional circuit components
2Manufacturing precision
If piston mode structures or additional circuit components are added to increase filter skirt steepness, then the steepness specification is met, but the device complexity increases
Solution Approach 1:
The filter structure serves itself by using the inherent transverse spurious mode of the narrow aperture IDT to achieve filter skirt steepness. The design eliminates the need for external piston mode structures or additional circuit components by making the resonator's own spurious mode work in favor of the filter performance
Solution Approach 2:
By changing the IDT aperture parameter to less than 10 wavelengths, the patent achieves filter skirt steepness through the resonator's intrinsic characteristics rather than adding external structures, thereby maintaining device simplicity while meeting steepness specifications
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 allows for increased skirt steepness in acoustic wave filters, reducing insertion loss and improving rejection of frequencies close to the passband, thereby meeting stringent specifications in wireless communication systems without the need for additional circuit components.
Implementation Method 1
A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer
Implementation Method 2
An acoustic wave filter can include a plurality of resonators arranged to filter a radio frequency signal
Data Source
AI summary
Aspects of this disclosure relate to an acoustic wave filter with an acoustic wave resonator arranged to concentrate a transverse spurious mode at a frequency. Such an acoustic wave resonator can have a narrow aperture to concentrate the transverse spurious mode. The transverse spurious mode can increase steepness of a skirt of the acoustic wave filter. Related methods, acoustic wave devices, multiplexers, radio frequency front ends, radio frequency modules, and wireless communication devices are disclosed.