RF Filter Shunt Resonator Tuning for 3 GHz Spurious Suppression
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Solution Overview
Problem
Current RF filters face performance degradation at higher frequencies above 3 GHz due to unwanted spurious excitations, particularly bulk waves in electroacoustic resonators, leading to inadequate isolation, insertion loss, bandwidth, pass band skirts, and attenuation outside the pass band.
Innovation Solution
The RF filter design incorporates a combination of series and shunt resonators, where at least one shunt resonator is replaced with a capacitor or an electroacoustic resonator paired with a de-tuning coil, shifting unwanted parasitic effects to frequencies that enhance out-of-band suppression and improve filter characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electroacoustic resonators are used in RF filters, then steep pass band skirts and high rejection are achieved, but unwanted spurious excitations occur at higher frequencies above 3 GHz
Solution Approach 1:
The patent converts the harmful spurious excitations generated by electroacoustic resonators into beneficial effects by strategically positioning them to enhance out-of-band suppression. The method involves designing the filter so that spurious modes occur at frequencies where they provide additional attenuation, transforming a detrimental phenomenon into a useful feature for improving filter performance at higher frequencies.
2Ease of manufacture
If known RF filter designs are used, then manufacturing simplicity is maintained, but performance degrades at frequencies above 3 GHz
Solution Approach 1:
The patent applies parameter changes by modifying the resonance frequencies and Q-factors of individual resonators, adjusting coupling coefficients between resonators, and changing the topology of the filter network. These parameter adjustments enable the filter to maintain optimal performance at higher frequencies above 3 GHz while preserving the manufacturability of the design through standard fabrication processes.
3Reliability
If more resonators are added to improve isolation and attenuation, then filter performance improves, but device complexity increases
Solution Approach 1:
The patent makes each resonator and coupling element perform multiple functions simultaneously. For example, resonators provide both signal transmission in the passband and spurious mode generation for out-of-band suppression. The coupling structures serve both to transfer signals between resonators and to control the positioning of spurious modes. This multi-functionality achieves improved isolation and attenuation without proportionally increasing device complexity.
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 converts detrimental parasitic effects into beneficial ones, enhancing the filter's performance by shifting unwanted frequencies outside the pass band, thereby achieving improved isolation and attenuation, especially at higher frequencies.
Implementation Method 1
In such electroacoustic resonators the piezoelectric effect is utilized to convert between RF signal and acoustic waves.
Data Source
AI summary
A filter and a method for forming a filter are disclosed. In an embodiment a filter includes a first port, a second port and a signal path between the first port and the second port. The filter further includes a plurality of series resonators electrically connected in series in the signal path, a plurality of shunt paths, each electrically connecting the signal path to ground and one parallel resonator electrically connected in each shunt path, wherein at least one series resonator is an electroacoustic resonator, and wherein at least one parallel resonator comprises one acoustically inactive capacitor or an electrical connection of an acoustically active resonator and a de-tuning coil.