Extracted-Pole Ladder Filter for Steeper RF Band Edges
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Solution Overview
Problem
Current radio frequency (RF) filters face challenges in achieving improved performance at higher frequencies while maintaining manufacturing efficiency, particularly in ensuring precise frequency selectivity and rejection across various frequency bands.
Innovation Solution
A bandpass filter design incorporating bulk acoustic resonators with specific configurations, including piezoelectric layers, interdigital transducers, and varying dielectric and stack thicknesses, along with extracted pole resonators, to enhance frequency selectivity and rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional RF filter designs are used, then manufacturing simplicity is maintained, but frequency selectivity and rejection performance deteriorate at higher frequencies
Solution Approach 1:
The filter is divided into multiple functional sections: series resonators for passband definition, shunt resonators for stopband rejection, and extracted pole resonators for enhanced edge steepness. Each segment performs a specific function, allowing independent optimization of frequency selectivity while maintaining overall manufacturing feasibility through modular assembly
Solution Approach 2:
Different resonator types are strategically placed at different locations within the filter structure. Series resonators are positioned in series arms, shunt resonators in shunt arms, and extracted pole resonators specifically at band edges. Each location receives a resonator configuration optimized for its specific functional requirement, achieving superior local frequency selectivity
2Manufacturing precision
If extracted pole resonators are added to improve band edge steepness, then frequency selectivity is improved, but device complexity increases
Solution Approach 1:
The extracted pole resonators are deliberately positioned outside the main passband frequency range, with their resonance frequencies tuned to lie just beyond the band edges. This extraction of pole locations to specific strategic positions enables enhanced band edge steepness by creating transmission zeros at critical frequencies, improving selectivity without interfering with the main passband operation
Solution Approach 2:
The extracted pole resonators are pre-configured with specific resonance frequencies positioned beyond the passband edges during the design phase. This preliminary positioning of poles and zeros creates the desired band edge steepness characteristics before the filter is assembled, ensuring optimal frequency selectivity is achieved through careful pre-planning of resonator parameters
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 design achieves improved frequency selectivity and rejection, enabling operation across broader frequency bands with reduced manufacturing complexity and increased performance.
Implementation Method 1
an interdigital transducer (IDT) on the piezoelectric layer and having a plurality of interleaved fingers
Implementation Method 2
a plurality of bulk acoustic resonators that each comprise a piezoelectric layer
Data Source
AI summary
A bandpass filter is provided that includes a plurality of bulk acoustic resonators. Each resonator includes a piezoelectric layer, an interdigital transducer (IDT) on the piezoelectric layer, and a dielectric layer disposed on and between interleaved fingers of the IDT. Moreover, the plurality of bulks acoustic resonators includes series resonators connected in series between an input and an output of the bandpass filter, shunt resonators connected between a ground and a node between a respective pair of the plurality of series resonators, a first extracted pole resonator connected between the ground and a node between the input and a first series resonator, and a second extracted pole resonator connected between the ground and a node between the output and a last series resonator. One of the extracted pole resonators has a resonance frequency that is higher than an upper edge of a passband of the bandpass filter.