RF Filter Topology for Sharp Attenuation and Low Pass-Band Loss
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Solution Overview
Problem
Existing radio frequency filters with acoustic wave resonators face limitations in achieving a sharp attenuation characteristic and low-loss pass band due to the constraints imposed by the resonant band width of acoustic wave resonators.
Innovation Solution
A radio frequency filter design incorporating two series-connected impedance elements, a parallel-connected second impedance element, and a parallel-arm resonator between the ground and a node between the impedance elements, allowing for a low-loss pass band and sharp attenuation characteristic without being limited by the resonant band width of acoustic wave resonators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If acoustic wave resonators are arranged in a ladder shape to achieve sharp attenuation characteristic, then the filter has sharp attenuation characteristic, but the pass band is limited by the resonant band width of the acoustic wave resonators and insertion loss increases
Solution Approach 1:
The filter is divided into multiple functional sections: series impedance elements (first and second) for defining pass band characteristics, parallel impedance elements for attenuation, and acoustic wave resonators strategically placed only where needed for stop band rejection. This segmentation allows the pass band to be determined by LC resonance rather than acoustic resonator bandwidth, reducing insertion loss while maintaining sharp attenuation where required.
Solution Approach 2:
Acoustic wave resonators are not uniformly distributed but strategically positioned only in specific parallel arm positions where sharp attenuation is required. The series arm elements use simple LC components with low loss, while parallel arm elements use acoustic resonators for targeted attenuation. This local differentiation optimizes both pass band performance and stop band rejection.
2Adaptability or versatility
If the pass band is made wider than the resonant band width of acoustic wave resonators, then a wider frequency range is covered, but insertion loss in the pass band increases
Solution Approach 1:
The patent changes the determining factor for pass band width from acoustic resonator resonant band width to the resonance characteristics of the LC circuit formed by series impedance elements and parallel impedance elements. By adjusting LC component values rather than acoustic resonator parameters, the pass band can be widened without the proportional increase in insertion loss that would occur with acoustic resonators.
3Device complexity
If acoustic wave resonators are used to define the pass band, then the filter structure is simple, but the pass band is constrained by the resonant band width of the resonators
Solution Approach 1:
The patent creates a hybrid filter structure where LC circuits provide pass band definition and acoustic wave resonators provide stop band attenuation. This multi-functional approach allows the same filter to achieve both wide adjustable pass bands (via LC tuning) and sharp rejection (via acoustic resonators), making the structure more versatile than using acoustic resonators alone.
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 solution enables a radio frequency filter with a sharp attenuation characteristic and a low-loss pass band that is not constrained by the resonant band width of acoustic wave resonators, improving performance compared to traditional designs.
Implementation Method 1
a parallel-arm resonator that is connected between a ground and a node between the two first impedance elements on the path
Implementation Method 2
Each of the first impedance elements is one of a capacitor and an inductor, and the second impedance element is the other one of the capacitor and the inductor
Data Source
AI summary
A filter (10) includes two capacitors (C1a and C1b) that are connected in series on a path connecting an input terminal (101a) and an output terminal (102a), an inductor (L2) that is connected in parallel with a series circuit including the two capacitors (C1a and C1b), and a parallel-arm resonator (P1) that is connected between the ground and a node (N) between the two capacitors (C1a and C1b) on the path.