Ladder Filter Inductor Layout for Wider Passband in Less Space
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Solution Overview
Problem
Existing ladder filters face challenges in achieving a wide pass band and reduced size, as increasing inductance for wider fractional bandwidth results in larger filter devices.
Innovation Solution
A filter device design incorporating a first resonator with the largest fractional bandwidth, connected in series with an inductor, and second resonators with smaller inductors to widen the pass band while minimizing device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If inductance of the inductor is increased to increase fractional bandwidth, then the value of fractional bandwidth is improved, but the size of the inductor and filter device becomes larger
Solution Approach 1:
The patent applies local quality by differentiating the inductance values assigned to different resonators based on their specific fractional bandwidth requirements. The first resonator is assigned a first inductance value while the second resonator is assigned a second inductance value that is smaller, allowing each component to be optimized locally rather than using a uniform inductance value throughout the filter device.
Solution Approach 2:
The patent changes the inductance parameter selectively across different resonators. By varying the inductance value from the first resonator to the second resonator, the patent achieves different fractional bandwidth characteristics for each resonator, thereby widening the overall pass band without requiring all inductors to be large.
2Speed
If acoustic wave resonators with small fractional bandwidth are used, then steepness at end portion of pass band is improved, but the pass band becomes narrow
Solution Approach 1:
The patent applies local quality by assigning different inductance values to different resonators positioned at different locations in the filter circuit. The first resonator with its first inductance value provides steepness at the pass band end, while the second resonator with its smaller second inductance value contributes to expanding the pass band width.
Solution Approach 2:
The patent uses asymmetry by deliberately making the inductance values unequal between the first and second resonators. This asymmetric configuration allows the filter to achieve both steep rolloff characteristics and wide pass band simultaneously, as each resonator contributes differently to the overall frequency response.
Data Source
AI summary
A filter device includes resonators including at least one series arm resonator and at least one parallel arm resonator. The resonators include a parallel arm resonator defining and functioning as a first resonator with a largest fractional bandwidth among the resonators, and at least one second resonator. The filter device includes an inductor connected in series to the first resonator.