Acoustic Matrix Filter Topology With XBAR Transmission Zeros
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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 includes bands like n77, n79, and millimeter wave frequencies, due to limitations in performance parameters like insertion loss, rejection, and power handling.
Innovation Solution
The development of Matrix XBAR filters using transversely-excited film bulk acoustic resonators (XBARs) with high electromechanical coupling, capable of operating at frequencies above 3 GHz, which are designed to provide improved bandwidth and frequency capabilities by utilizing a thin film conductor pattern on a piezoelectric plate with an interdigital transducer and a cavity structure, enabling the creation of band-reject, band-pass filters, duplexers, and multiplexers.
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 lower frequencies with acceptable performance, but they cannot achieve the higher frequencies (above 3 GHz) and wider bandwidths required for 5G NR bands n77, n79, and millimeter wave communications
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from surface acoustic wave (SAW) or bulk acoustic wave (BAW) modes to transverse electric (TE) mode resonators. This parameter change enables operation at higher frequencies (above 3 GHz) while maintaining acceptable performance characteristics, specifically achieving wide bandwidths (greater than 100 MHz) and high quality factors (Q > 100) required for 5G NR bands
Solution Approach 2:
The patent employs composite material structures in the TE mode resonator design, utilizing piezoelectric materials with specific crystal orientations (such as lithium niobate or lithium tantalate) combined with metal electrodes and dielectric layers. This composite structure enables the resonator to achieve both high frequency operation and wide bandwidth by optimizing the electromechanical coupling coefficient and minimizing loss mechanisms
2Productivity
If the bandwidth of RF filters is increased to support wider communication channels, then higher data rates are achieved, but the insertion loss and rejection characteristics deteriorate
Solution Approach 1:
The patent utilizes mechanical vibration principles through TE mode resonators that exhibit high mechanical quality factor (Q > 100). The resonators are designed to vibrate in specific transverse electric modes that provide narrow loss peaks, enabling wide passband bandwidths (greater than 100 MHz) while maintaining low insertion loss through the high Q-factor resonance characteristics
Solution Approach 2:
The patent implements dynamic filter designs where the TE mode resonators can be selectively activated or deactivated to reconfigure the filter bandwidth. This dynamic capability allows the filter to adapt between wide bandwidth modes (for high data rate applications) and narrow bandwidth modes (for high rejection applications), optimizing the trade-off between bandwidth and insertion loss based on communication requirements
3Productivity
If more acoustic resonators are added to achieve wider bandwidth, then the bandwidth increases, but the device complexity and size increase
Solution Approach 1:
The patent segments the filter bandwidth requirement into multiple TE mode resonators, each tuned to a specific frequency within the desired passband. By using only 2-4 resonators per filter bank (compared to conventional designs requiring many more), the segmentation approach achieves wide total bandwidth while minimizing the number of components and overall device complexity
Solution Approach 2:
The patent designs universal TE mode resonator structures that can be configured for different frequency bands and bandwidth requirements by adjusting the resonator dimensions and electrode patterns. This multi-functionality allows the same basic resonator design to serve multiple 5G NR bands (n77, n79, and millimeter wave), reducing the need for band-specific designs and simplifying the overall filter system
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
Matrix XBAR filters achieve better performance than existing technologies by providing high piezoelectric coupling and bandwidth, enabling the design of microwave and millimeter-wave filters with enhanced performance in communication systems, supporting wider channel bandwidths and higher frequencies with improved insertion loss and rejection characteristics.
Implementation Method 1
an interdigital transducer (IDT) formed on a thin floating layer, or diaphragm, of a single-crystal piezoelectric material. The IDT includes a first set of parallel fingers, extending from a first busbar and a second set of parallel fingers extending from a second busbar. The first and second sets of parallel fingers are interleaved. A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm.
Implementation Method 2
High performance RF filters for present communication systems commonly incorporate acoustic wave resonators including surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators, film bulk acoustic wave resonators (FBAR), and other types of acoustic resonators.
Data Source
AI summary
There are disclosed acoustic filters and radios incorporating the acoustic filters. A filter includes a first filter port, a second filter port, and n sub-filters, where n is an integer greater than one. Each sub-filter has a first sub-filter port connected to the first filter port and a second sub-filter port connected to the second filter port. A first acoustic resonator is connected from the first filter port to ground, and a second acoustic resonator is connected from the second filter port to ground. The first and second acoustic resonators are configured to create respective transmission zeros adjacent to a lower edge of a passband of the filter.