BAW Filter Topology for Second Harmonic Suppression
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Solution Overview
Problem
Bulk acoustic wave (BAW) resonators experience non-linearity at high power levels, leading to the generation of undesirable second harmonic emissions (H2) in radio frequency filters.
Innovation Solution
The implementation of anti-series pairs of BAW resonators with reversed electrode polarization and a balancing capacitor connected to their common electrode, along with additional resonator splits and passive impedance elements, to compensate for parasitic capacitance and electromagnetic coupling, effectively suppressing second harmonic emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If BAW resonators operate at high power levels, then filtering capability is maintained, but second harmonic emissions are generated
Solution Approach 1:
The patent divides a single BAW resonator into multiple resonators (at least two) with different acoustic path lengths. This segmentation allows each resonator to contribute differently to the overall filtering function while suppressing second harmonic emissions through destructive interference of the harmonic components generated at different power levels
Solution Approach 2:
The patent employs asymmetric design by configuring resonators with different acoustic path lengths rather than identical symmetric structures. This asymmetry enables differential phase shifts for fundamental and harmonic frequencies, allowing the filter to maintain power handling capability while rejecting second harmonic emissions through phase-based cancellation
2Object-generated harmful factors
If multiple resonators with different acoustic path lengths are used, then second harmonic emissions are suppressed, but device complexity increases
Solution Approach 1:
The patent combines multiple resonators with different acoustic path lengths into a single integrated filter structure where all resonators share common electrodes and are coupled to the same input and output ports. This merging approach achieves second harmonic suppression through the diverse path lengths while avoiding the complexity of completely separate filter structures
Solution Approach 2:
The patent makes each resonator serve multiple functions: they all contribute to fundamental frequency filtering while simultaneously participating in second harmonic suppression through their different acoustic characteristics. This multi-functionality reduces overall device complexity by eliminating the need for separate harmonic rejection stages
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 configuration significantly reduces and cancels second harmonic emissions, providing higher rejection levels compared to previous suppression techniques, enhancing the performance of BAW filters in radio frequency systems.
Implementation Method 1
In BAW resonators, acoustic waves propagate in a bulk of a piezoelectric layer
Implementation Method 2
The capacitor is configured to compensate for a mismatch in parasitic capacitance between the first pair of bulk acoustic wave resonators and the second pair of bulk acoustic wave resonators
Data Source
AI summary
Aspects of this disclosure relate to acoustic wave filters with second harmonic emission suppression. In an embodiment, an acoustic wave filter includes a first pair of bulk acoustic wave resonators in anti-series with each other and a second pair of bulk acoustic wave resonators in anti-series with each other. The second pair of bulk acoustic wave resonators has reverse electrode polarization relative to the first pair of bulk acoustic wave resonators. The first pair of bulk acoustic wave resonators is in series with the second pair of bulk acoustic wave resonators. Other embodiments of acoustic wave filters with second harmonic emission suppression are disclosed. Related multiplexers, radio frequency modules, wireless communication devices, and methods are disclosed.