Acoustic Filter Resonator Tuning for a Steeper Lower Passband Edge
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Solution Overview
Problem
Current RF filters operating at specific frequencies, such as Wi-Fi 6, require a steep lower passband edge to reject neighboring frequency bands, but achieving this with conventional designs necessitates large-scale circuitry.
Innovation Solution
The proposed solution involves a filter device with at least two series resonators and three shunt resonators, where the shunt resonator with the highest resonance frequency has the smallest capacitance value and IDT area, allowing for a steep lower passband edge without the need for large-scale circuity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional filter designs are used to achieve a steep lower passband edge, then the filter can reject neighboring frequency bands effectively, but the circuitry becomes large-scale and complex
Solution Approach 1:
The patent changes the capacitance values of shunt resonators to achieve a steep lower passband edge. Specifically, the first shunt resonator has a first capacitance value and the second shunt resonator has a second capacitance value that is different from the first, allowing optimization of the passband edge steepness without requiring large-scale circuitry. This parameter optimization enables the filter to meet Wi-Fi 6 rejection requirements while maintaining a compact design.
2Manufacturing precision
If the operating frequency of shunt resonator is raised and area is decreased, then the steepness of lower passband edge increases, but the capacitance value must be reduced
Solution Approach 1:
The patent simultaneously optimizes multiple parameters of the shunt resonators including capacitance value, area, and operating frequency. The first shunt resonator has a first capacitance value and the second shunt resonator has a second capacitance value, with their areas and frequencies adjusted accordingly. This coordinated parameter change achieves steep passband edge while managing capacitance requirements.
Solution Approach 2:
The patent applies different characteristics to different shunt resonators within the filter circuit. The first shunt resonator has distinct capacitance, area, and frequency parameters compared to the second shunt resonator. This local differentiation allows each resonator to contribute optimally to the overall filter response, achieving steep passband edge through localized parameter optimization rather than uniform design.
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 configuration effectively increases the steepness of the lower passband edge, improving the filter's ability to reject neighboring frequency bands while maintaining a compact circuit design.
Implementation Method 1
a piezoelectric layer attached either directly or via one or more intermediate layers to the substrate, and an interdigital transducer (IDT) at the piezoelectric layer
Implementation Method 2
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 3
The transversely-excited film bulk acoustic resonator (XBAR) is an acoustic resonator structure for use in microwave filters
Data Source
AI summary
A filter device is provided that includes series resonators connected between a pair of ports; and shunt resonators that are each connected between a ground connection and a node between the series resonators. A shunt resonator having a highest resonance frequency of the shunt resonators has a smallest capacitance value of the shunt resonators. Moreover, the resonators each include a piezoelectric layer attached either directly or via one or more intermediate layers to the substrate, and an interdigital transducer (IDT) at the piezoelectric layer and that includes a plurality of interleaved fingers.