BAW Filter Parallel Resonator Layout for Second Harmonic Cancellation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional bulk acoustic wave filters generate significant second harmonics due to piezoelectric layer nonlinearities, which are not effectively canceled by existing filter implementation techniques.
Innovation Solution
The implementation of a bulk acoustic wave filter design using two half-area filter circuits connected in parallel, where at least two resonators in each circuit are reverse connected relative to each other, effectively canceling out second harmonic emissions by opposing phases and amplitudes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a single full-area FBAR is used in the filter, then the filter achieves normal impedance and performance, but significant second harmonics are generated due to piezoelectric layer nonlinearities
Solution Approach 1:
The patent divides a single full-area FBAR into two half-area FBARs connected in parallel. Each half-area FBAR generates second harmonics with opposite phase due to reverse electrode connections, causing the harmonics to cancel each other out while maintaining the overall filter impedance and performance
Solution Approach 2:
The patent reverses the electrode connections of one FBAR in the parallel pair relative to the other. This inversion causes the piezoelectric nonlinearities to generate second harmonics with opposite phases, enabling harmonic cancellation while preserving the normal filter operation
2Object-generated harmful factors
If antiparallel connected FBARs are used to cancel second harmonics, then harmonic cancellation is achieved, but the filter implementation becomes more complex with multiple connection options
Solution Approach 1:
The patent combines two half-area FBARs with reverse electrode connections in a parallel configuration. This merging approach integrates harmonic cancellation functionality directly into the filter structure, eliminating the need for separate harmonic suppression circuits while maintaining simple parallel connection topology
3Object-generated harmful factors
If multiple FBARs are replaced with antiparallel pairs, then second harmonics are reduced, but the manufacturing and assembly process becomes more difficult
Solution Approach 1:
The patent segments the filter design into modular half-area FBAR units that can be independently fabricated and then assembled in parallel. This segmentation enables standardized manufacturing processes for each half-area unit while simplifying the overall assembly through repetitive parallel connections
Solution Approach 2:
The patent changes the area parameter of individual FBARs from full-area to half-area while compensating through parallel connection. This parameter change maintains equivalent impedance characteristics and simplifies the fabrication process by using smaller, more manageable resonator dimensions
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 design achieves reduced second harmonics generation while maintaining similar performance to traditional full-area filters, with equivalent impedance and chip area usage, effectively mitigating harmonic interference.
Implementation Method 1
The first plurality of resonators generally comprise piezoelectric material. The second plurality of resonators generally comprise piezoelectric material.
Implementation Method 2
The 2nd harmonics generated in the normally connected FBAR and the 2nd harmonics generated in the reverse connected FBAR in the anti-parallel connected pair of FBARs will have the same amplitude but opposite phases, causing the 2nd harmonics generated by the antiparallel FBARs to essentially cancel out.
Data Source
AI summary
An apparatus includes a first filter and a second filter. The first filter generally comprises a first plurality of resonators. The second filter generally comprises a second plurality of resonators. The first plurality of resonators generally comprise piezoelectric material. The second plurality of resonators generally comprise piezoelectric material. At least two of the first plurality of resonators are arranged in series between a signal input of the first filter and a signal output of the first filter. At least two of the second plurality of resonators are arranged in series between a signal input of the second filter and a signal output of the second filter. The second plurality of resonators are reverse connected relative to the first plurality of resonators. The first filter is generally connected in parallel with the second filter such that (a) the signal input of the first filter is connected to the signal input of the second filter, (b) the signal output of the first filter is connected to the signal output of the second filter, and (c) second harmonic emissions of the first filter are substantially canceled by second harmonic emissions of the second filter. The apparatus generally comprises a bulk acoustic wave (BAW) filter.