Loaded Resonator Notches for LBAW Filter Sideband Suppression
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Solution Overview
Problem
Lateral Bulk Acoustic Wave (LBAW) filters face challenges in suppressing parasitic sidebands, which affect their band pass filter characteristics, and existing solutions are complex and require multiple piezoelectric layers or reflectors.
Innovation Solution
Incorporating additional acoustic resonators in parallel with the LBAW filter, which have impedance notches at specific frequencies within the sideband range, to increase insertion loss and suppress sidebands, thereby improving the band pass response without the need for multiple piezoelectric layers or reflectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional acoustic resonators are added in parallel with the LBAW filter, then sideband suppression is improved, but device complexity increases
Solution Approach 1:
The patent divides the sideband suppression function into multiple independent resonators, each targeting specific sideband frequencies. By segmenting the suppression task across multiple parallel resonators with different quality factors and impedance characteristics, the system achieves comprehensive sideband rejection while maintaining modular design flexibility.
Solution Approach 2:
The patent utilizes parameter changes by varying the quality factor, impedance, and resonant frequency of each parallel resonator. These parameter adjustments allow each resonator to contribute differently to sideband suppression at specific frequencies, enabling precise control over the filter's frequency response characteristics.
2Reliability
If resonators with different quality factors are used, then sideband suppression effectiveness is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies local quality by assigning different quality factors to different resonators based on their specific functional requirements. Each resonator is optimized with appropriate damping characteristics tailored to its role in suppressing specific sidebands, rather than using uniform quality factors across all resonators.
Solution Approach 2:
The patent employs parameter changes by systematically varying the quality factor as a key design parameter for each resonator. This allows optimization of sideband suppression effectiveness at different frequencies while establishing clear design guidelines that can accommodate normal manufacturing tolerances.
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 sidebands, enhancing the band pass filter characteristics of LBAW filters, simplifying fabrication, and allowing operation at higher frequencies with wider bandwidths and smaller size.
Implementation Method 1
LBAWs can be used as band pass filters. The band pass filter may include one or more undesired (or parasitic) sidebands. Implementations of the present disclosure provide techniques to suppress the undesired sidebands by adding one or more acoustic resonators in parallel with the LBAW.
Implementation Method 2
By applying an alternating voltage across the piezoelectric layer at the input resonator, a mechanical resonance is formed in the piezoelectric layer below the input electrode. The piezoelectric layer thickness and the gap between electrodes can be designed such that this mechanical resonance is coupled across the gap to the output resonator.
Implementation Method 3
Incorporating additional acoustic resonators in parallel with the LBAW filter, which have impedance notches at specific frequencies within the sideband range, to increase insertion loss and suppress sidebands
Data Source
AI summary
An acoustic wave filter device is disclosed. The device includes an acoustic wave filter element, and a first resonator and a second resonator coupled to the acoustic wave filter element. The acoustic wave filter element includes interdigitated input electrodes and output electrodes located on a top surface of a piezoelectric layer and an counter-electrode on the bottom surface of the piezoelectric layer. Each of the first and the second resonators includes a resonator electrode on the top surface of the piezoelectric layer and a resonator counter-electrode on the bottom surface of the piezoelectric layer. The first resonator has a first notch in resonator impedance at a first frequency. The second resonator includes a first mass loading layer on the second resonator electrode such that the second resonator has a second notch in resonator impedance at a second frequency that is different from the first frequency.