Half-Lattice Micro-Acoustic RF Filter for Broad Bandwidth and Steep Skirts
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Solution Overview
Problem
Existing RF filters struggle to achieve a broad passband and good out-of-band attenuation while maintaining a simple manufacturing process, particularly for 5G communication standards like n79 and n77 bands, due to limitations in ladder-type designs and complex fabrication methods.
Innovation Solution
A micro-acoustic RF filter with a half-lattice structure incorporating phase shifters and resonators, allowing for a broad passband and steep filter skirts, using micro-acoustic resonators and capacitors to reduce spurious modes, and enabling independent design of passband and stopband performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If ladder-type filter structure is used, then bandwidth can be increased by adding passive components, but out-of-band attenuation deteriorates
Solution Approach 1:
The filter is divided into two independent sections: a first ladder-type section for passband signal transmission and a second lattice-type section for stopband signal rejection. This segmentation allows each section to be optimized for its specific function, with the lattice section providing superior out-of-band attenuation while the ladder section maintains broad passband coverage.
Solution Approach 2:
A coupling resonator is introduced as an intermediary element between the first and second sections. This coupling resonator enables energy transfer between the ladder-type and lattice-type sections while maintaining their functional independence, allowing the broad bandwidth of the ladder section to be combined with the sharp rejection of the lattice section.
2Speed
If scandium doping is used to increase acoustic coupling, then bandwidth improves, but fabrication complexity increases
Solution Approach 1:
The invention changes the structural configuration parameter from traditional ladder-type to a hybrid structure combining ladder and lattice sections. This parameter change achieves broadband performance through the lattice section's inherent properties rather than relying on material parameter changes like scandium doping, thereby avoiding fabrication complexity while maintaining bandwidth.
3Speed
If ladder-type structure is used for broad passband, then passband width increases, but filter skirt steepness deteriorates
Solution Approach 1:
The filter response is segmented into passband and stopband regions, with the first ladder-type section controlling passband characteristics and the second lattice-type section controlling stopband characteristics. This segmentation enables independent optimization of passband width and filter skirt steepness without mutual interference.
Solution Approach 2:
The coupling resonator acts as a mediator that transitions the signal between the ladder-type and lattice-type sections. It enables the signal to experience the broad passband of the ladder section while subsequently experiencing the sharp rejection of the lattice section, achieving both broad passband and steep filter skirts.
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 proposed filter achieves a broad passband with good out-of-band attenuation, meeting 5G communication requirements, and can be manufactured using standard technologies for surface and bulk acoustic wave resonators, providing flexibility in impedance matching and filter design.
Implementation Method 1
the use of passive components such as inductors in the ladder-type structure may increase the bandwidth, however, at the cost of overall filter performance such as poor out-of-band attenuation
Implementation Method 2
One of the first and second signal paths furthermore comprises a phase shifter connected in series with the resonator. The phase shifter is configured to perform a phase shift of 180° or of about 180°
Data Source
AI summary
A micro-acoustic RF filter comprises first and second ports (101, 102). First and a second signal paths (120, 110) are coupled between the first and second ports and include a corresponding resonator (111, 121). The resonator of at least one of the signal paths is a micro-acoustic resonator. One of the signal paths includes also a phase shifter (232) serially connected with the resonator (111). The micro-acoustic RF filter achieves a broad passband determined by the resonance frequencies of the micro-acoustic resonators. The filter allows flexible adaption of the passband and stopband performance.