Acoustic Wave Filter Using Longitudinal Modes for Out-of-Band Rejection
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Solution Overview
Problem
Designing acoustic wave filters with improved out of band rejection is challenging due to the interference of spurious modes, which are typically suppressed to minimize their effect on filter properties.
Innovation Solution
Enhance the spurious modes of resonators, particularly through the use of shunt resonators with unsuppressed longitudinal modes, to improve out of band rejection without adding additional resonators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spurious modes are suppressed in resonators, then filter properties are minimized and passband performance is improved, but out of band rejection is degraded
Solution Approach 1:
The patent converts the harmful spurious longitudinal modes into beneficial elements by intentionally designing shunt resonators where these modes are unsuppressed. The spurious modes that normally degrade out of band rejection are instead utilized to provide additional attenuation in out of band regions, thereby improving overall filter performance while maintaining passband characteristics
Solution Approach 2:
The patent changes the parameter of mode suppression by designing shunt resonators with specific physical dimensions (length, width, substrate properties) that result in unsuppressed longitudinal modes. By adjusting resonator geometry and substrate characteristics, the spurious modes are transformed from harmful interference into useful attenuation mechanisms in out of band regions
2Object-affected harmful factors
If additional resonators are added to improve out of band rejection, then filter performance is enhanced, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent makes existing shunt resonators multi-functional by designing them to simultaneously define passband edges and provide out of band rejection. The shunt resonators perform dual functions: their primary mode defines the lower passband edge while their unsuppressed longitudinal modes provide additional attenuation in out of band regions, eliminating the need for separate resonators dedicated solely to rejection
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
Broadens suppression in the out of band region, allowing for finer tuning of the pass band edge and reducing the number of resonators needed, thus enhancing filter performance.
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 interdigital transductor electrode on a piezoelectric substrate
Implementation Method 3
Acoustic wave filters can be implemented in radio frequency electronic systems. An acoustic wave filter can be a band pass filter.
Data Source
AI summary
According to the present disclosure, an acoustic wave filter is provided. The acoustic wave filter has a pass band and is configured to filter a radio frequency signal. The acoustic wave filter comprises a series resonator and a shunt resonator, the shunt resonator having a primary mode defined by a resonant frequency of the shunt resonator and a secondary mode defined by a longitudinal mode of the shunt resonator, the primary mode defining a lower edge of the pass band and the secondary mode being of a higher frequency than the primary mode. A corresponding radio-frequency module and wireless mobile device comprising said acoustic wave filter are also provided.