Electromechanical Filter Resonator Asymmetry for Spur Attenuation
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Solution Overview
Problem
Electroacoustic resonators, such as those using aluminum nitride, suffer from signal degradation due to undesired spurious responses, which are not effectively mitigated by existing resonator architectures, leading to interference with desired signal processing and sensing functions.
Innovation Solution
The solution involves electrically connecting resonators with different physical geometries, such as varying numbers of electrode fingers, to create overlapping center frequencies while offsetting spurious resonances, thereby attenuating them in the filter output and reinforcing the desired response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If identical resonators are used in a filter, then the desired center frequency response is reinforced, but spurious responses are also reinforced and not attenuated
Solution Approach 1:
The patent applies asymmetry by using resonators with different physical geometries (different numbers of electrode fingers) in the filter. Specifically, first and second resonators have different numbers of electrode fingers, creating asymmetric structures that produce different spurious response frequencies while maintaining the same center frequency, thereby attenuating spurious responses through destructive interference
Solution Approach 2:
The patent changes physical parameters of the resonators, specifically the number of electrode fingers, to alter the mode shapes and spurious response frequencies. By varying this parameter while keeping the center frequency substantially the same, the patent achieves spurious response attenuation without sacrificing the desired signal reinforcement
2Object-generated harmful factors
If resonators with different physical geometries are used, then spurious responses are offset and attenuated, but the complexity of the filter design increases
Solution Approach 1:
The patent segments the filter into distinct resonator components with different geometries (first resonator with n1 electrode fingers, second resonator with n2 electrode fingers). This segmentation allows each resonator to be designed and fabricated independently with specific geometric variations, simplifying the overall design process while achieving spurious response attenuation
Solution Approach 2:
The patent uses parameter changes (varying the number of electrode fingers) as a straightforward design variable that can be easily implemented in standard fabrication processes. This approach increases design freedom without significantly complicating the manufacturing process, as it involves simple geometric modifications rather than complex structural changes
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 significantly attenuates spurious responses by ensuring that spurious resonances appear at non-identical frequencies across different resonators, resulting in improved signal quality with greater than 50 dBc spurious response rejection over a wide frequency span.
Implementation Method 1
AlN is one example of a piezoelectric material that responds both electrically and mechanically to applied electric signals, and that can be formed into an electroacoustic resonator capable of modifying such signals
Implementation Method 2
an AlN microresonator can be designed to efficiently transduce to any of various desired modes, but transduction to the numerous undesired symmetric and anti-symmetric Lamb modes
Implementation Method 3
two or more resonators are electrically connected together to form a filter having a bandwidth and a center frequency. The connected resonators have center frequencies that substantially coincide
Data Source
AI summary
A spur cancelling, electromechanical filter includes a first resonator having a first resonant frequency and one or more first spurious responses, and it also includes, electrically connected to the first resonator, a second resonator having a second resonant frequency and one or more second spurious responses. The first and second resonant frequencies are approximately identical, but the first resonator is physically non-identical to the second resonator. The difference between the resonators makes the respective spurious responses different. This allows for filters constructed from a cascade of these resonators to exhibit reduced spurious responses.