BAW Resonator Ladder Filter for Fundamental Tone Suppression
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Solution Overview
Problem
Existing bulk acoustic wave resonators generate spurious signals due to the generation of fundamental tones alongside second overtones, degrading performance in radio frequency filters.
Innovation Solution
Aligning the resonant frequencies of series and shunt bulk acoustic wave resonators to suppress fundamental tones and enhance the generation of second overtones, using specific thicknesses of piezoelectric and electrode layers to create a ladder filter design that cancels out spurious signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bulk acoustic wave resonators generate acoustic waves at fundamental tones, then the resonators can operate at lower frequencies with simpler design, but spurious signals are generated that degrade filter performance
Solution Approach 1:
The patent converts the harmful fundamental tone generation into a beneficial feature by designing the resonator to operate at the second overtone frequency (approximately twice the fundamental frequency). The fundamental tone and its harmonics are intentionally suppressed through specific piezoelectric layer thickness selection, while the second overtone is enhanced to provide the desired acoustic wave generation at higher frequencies without spurious signals
Solution Approach 2:
The patent changes the operating parameter from fundamental tone frequency to second overtone frequency by adjusting the piezoelectric layer thickness. This parameter change shifts the resonant frequency relationship, allowing the resonator to operate at approximately twice the fundamental frequency while suppressing the fundamental tone and its harmonics, thereby eliminating spurious signals
2Reliability
If resonators operate at second overtones, then spurious signals are suppressed and filter performance improves, but the resonator design and manufacturing precision requirements increase
Solution Approach 1:
The patent establishes specific parameter ranges for piezoelectric layer thickness (e.g., 0.5-2.0 times the acoustic wavelength at the second overtone frequency) that enable second overtone operation. By defining these parameter ranges, the patent provides manufacturing guidelines that balance the need for precision with practical fabrication capabilities
Solution Approach 2:
The patent applies different thickness requirements to different layers: the piezoelectric layer thickness is specifically controlled to enable second overtone operation, while other layers (electrodes, substrates) have standard manufacturing tolerances. This localized precision requirement focuses manufacturing attention only where critical for achieving the desired frequency response
3Object-generated harmful factors
If fundamental tones are suppressed through resonator alignment, then spurious signal generation is reduced, but the filter design complexity increases
Solution Approach 1:
Instead of trying to eliminate fundamental tones from series and shunt resonators separately, the patent inverts the approach by aligning the resonant frequencies of series and shunt resonators to the same frequency point. This alignment causes the fundamental tones to cancel each other out through destructive interference, while the second overtones (which are out of phase between series and shunt) are enhanced, achieving spurious signal suppression through a simplified frequency alignment strategy
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
The solution effectively suppresses fundamental tone signals, allowing radio frequency filters to operate with improved performance and higher frequencies without manufacturing reliability issues.
Implementation Method 1
the plurality of series bulk acoustic wave resonators and the plurality of shunt bulk acoustic wave resonators each include piezoelectric material layers
Implementation Method 2
resonant frequencies of the fundamental tone of the plurality of series bulk acoustic wave resonators are aligned in frequency with resonant frequencies of the fundamental tone of the plurality of shunt bulk acoustic wave resonators
Data Source
AI summary
Aspects and embodiments disclosed herein include a radio frequency filter comprising a plurality of series bulk acoustic wave resonators and a plurality of shunt bulk acoustic wave resonators, the plurality of series bulk acoustic wave resonators and the plurality of shunt bulk acoustic wave resonators configured and arranged to generate acoustic waves at both fundamental tones and second overtones and to suppress signals associated with the acoustic waves at the fundamental tones, a passband of the radio frequency filter with a lowest insertion loss defined by the acoustic waves generated at the second overtones of the plurality of series bulk acoustic wave resonators and the plurality of shunt bulk acoustic wave resonators.