Split-Ladder XBAR Filter Layout for Wideband N77 Frequency Selectivity
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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 by future communication networks, such as 5G NR and Wi-Fi bands, due to limitations in frequency range and bandwidth capability.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with a split-ladder architecture and varying piezoelectric plate thicknesses and dielectric layers to achieve the necessary resonance and anti-resonance frequencies for band-pass filters, enabling broader bandwidth and improved filter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional acoustic wave resonators (SAW, BAW, FBAR) are used, then the filter structure is simple and manufacturing is easier, but the frequency range and bandwidth capability are insufficient for higher frequency communications
Solution Approach 1:
The filter is divided into multiple resonator stages (series and shunt resonators) connected in a ladder configuration. Each resonator is designed with specific piezoelectric plate thicknesses to target different frequency ranges within the passband, enabling the overall filter to achieve wide bandwidth capability through segmented frequency coverage
Solution Approach 2:
Different piezoelectric plate thicknesses are used in different resonators within the same filter structure. Specifically, series resonators have one thickness while shunt resonators have a different thickness, allowing each component to be locally optimized for its specific frequency role while contributing to the overall high-frequency performance
2Manufacturing precision
If multiple resonators with different piezoelectric plate thicknesses are used, then frequency selectivity and bandwidth are improved, but manufacturing precision requirements increase
Solution Approach 1:
The piezoelectric plate thickness parameter is systematically varied between series and shunt resonators to achieve the desired frequency response. This parameter change is designed to be within manufacturable tolerances while providing sufficient frequency separation to achieve the required 40 dB rejection at band edges
Solution Approach 2:
Each resonator type (series vs. shunt) is given a specific piezoelectric plate thickness optimized for its function. Series resonators use one thickness for their resonant frequency, while shunt resonators use a different thickness for their anti-resonant frequency, allowing local optimization without requiring extreme manufacturing precision across the entire device
3Adaptability or versatility
If higher frequency resonators are designed, then bandwidth capability improves, but spurious modes increase and filter performance deteriorates
Solution Approach 1:
The piezoelectric plate thickness is specifically optimized for each resonator type to control their frequency characteristics. Series resonators are designed with thickness for resonant operation while shunt resonators are designed with different thickness for anti-resonant operation, which suppresses spurious modes and improves filter performance in the passband
Solution Approach 2:
Instead of using the same resonator design for both series and shunt positions, the invention inverts the approach by using different piezoelectric plate thicknesses. This inversion allows shunt resonators to operate at anti-resonance frequencies that naturally suppress spurious modes while series resonators operate at resonant frequencies for maximum signal transmission
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 approach allows for the design of RF filters that can effectively handle higher frequencies and wider bandwidths, enhancing communication system performance by providing better frequency selectivity and reduced spurious modes, thus supporting advanced communication standards like 5G NR and Wi-Fi.
Implementation Method 1
a piezoelectric plate, and an interdigital transducer (IDT) coupled to the piezoelectric plate. 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
XBAR resonators provide very high electromechanical coupling and high frequency capability. XBAR resonators may be used in a variety of RF filters including band-reject filters, band-pass filters, duplexers, and multiplexers.
Data Source
AI summary
Band N77 bandpass filters include a first plurality of transversely-excited film bulk acoustic resonators (XBARs) on a first chip comprising a first rotated YX-cut lithium niobate piezoelectric plate having a thickness less than or equal to 535 nm, and a second plurality of XBARs on a second chip comprising a second rotated YX-cut lithium niobate piezoelectric plate having a thickness greater than or equal to 556 nm. A circuit card is coupled to the first chip and the second chip. The circuit card includes conductors for making electrical connections between the first chip and the second chip.