XBAR Matrix Filter Architecture for Wideband 5G RF Filtering
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequencies and wider bandwidths required in future communication networks, such as the 5G NR standard, which necessitates the development of more effective filtering solutions for frequencies above 3 GHz.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with interdigital transducers on a thin piezoelectric diaphragm, which provide high electromechanical coupling and frequency capability, is employed in matrix filter architectures to achieve improved performance across a broader frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators (SAW, BAW, FBAR) are used in RF filters, then the filters can operate at standard frequencies, but they cannot achieve the higher frequencies and wider bandwidths required for future communication networks above 3 GHz
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from longitudinal wave modes to shear wave modes in a transversely excited configuration. This parameter change enables the resonator to operate at higher frequencies (above 3 GHz) while maintaining the desired filter performance characteristics, directly resolving the frequency capability limitation of conventional resonators
2Adaptability or versatility
If conventional acoustic wave resonators are used, then the filter design is simpler, but the bandwidth and frequency capabilities are insufficient for 5G NR and other high-frequency communication standards
Solution Approach 1:
The patent employs a transversely excited film bulk acoustic resonator configuration where the excitation direction is perpendicular to the propagation direction of the acoustic wave. This dynamic configuration allows the resonator to achieve wider bandwidth operation and higher frequency capability compared to conventional longitudinally excited resonators, while the floating piezoelectric layer provides mechanical flexibility for optimized performance
3Speed
If higher frequency operation is achieved using conventional resonators, then the frequency capability improves, but the electromechanical coupling and overall filter performance deteriorate
Solution Approach 1:
The patent utilizes shear horizontal acoustic waves excited in a floating piezoelectric layer by interdigital transducers. The mechanical vibration mode is specifically chosen to maximize electromechanical coupling efficiency at high frequencies. The shear wave configuration provides strong coupling between the electrical and mechanical domains, resolving the energy loss issue that plagues conventional resonators operating at high frequencies
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
XBAR-based matrix filters offer enhanced performance by achieving better bandwidth and frequency capabilities, enabling effective filtering in higher frequency communication bands, including those defined by the 5G NR standard, with improved rejection and insertion loss characteristics.
Implementation Method 1
A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm
Implementation Method 2
The XBAR is an acoustic resonator structure for use in microwave filters... provide high electromechanical coupling and high frequency capability
Data Source
AI summary
Radio frequency filters. A radio frequency filter includes a substrate attached to a piezoelectric plate, portions of the piezoelectric plate forming a plurality of diaphragms spanning respective cavities in the substrate. A conductor pattern formed on the piezoelectric plate includes a plurality of interdigital transducers (IDTs) of a respective plurality of resonators, interleaved fingers of each IDT disposed on a respective diaphragm of the plurality of diaphragms. The conductor pattern connects the plurality of resonators in a matrix filter circuit including a first sub-filter and a second sub-filter, each sub-filter comprising two or more resonators from the plurality of resonators.