Acoustic Wave Filter Topology for Steeper Stop-Band Attenuation
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Solution Overview
Problem
Current band pass filters using acoustic wave resonators in LC high pass and low pass filters face limitations in achieving a steep attenuation characteristic, particularly at the low frequency end of the stop band.
Innovation Solution
A filter device is designed with a series arm resonator and a parallel arm resonator, along with an inductor, to create resonance circuits that form an attenuation pole at the high frequency end of the stop band, improving the steepness of the attenuation characteristic by incorporating a sub-resonant frequency higher than the resonant frequency of the parallel arm resonator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a band pass filter using acoustic wave resonators in LC high pass and low pass filters is used, then the attenuation characteristic of the pass band is improved, but the steepness of the attenuation characteristic at the low frequency end of the pass band (high frequency end of the stop band) is insufficient
Solution Approach 1:
The filter is divided into multiple functional sections: a first filter with specific cutoff frequency, a series arm resonator, a parallel arm resonator, and an inductor. Each segment contributes to forming attenuation poles at different frequencies, collectively achieving the desired steep attenuation characteristic without requiring a completely complex redesign of the entire filter structure.
Solution Approach 2:
The parallel arm resonator is specifically configured with its resonant frequency to create an attenuation pole at the high frequency end of the stop band. The series arm resonator and inductor combination is designed to produce a sub-resonant frequency higher than the parallel arm resonator's resonant frequency. This localized optimization of specific components achieves steep attenuation at the critical frequency point without compromising overall filter performance.
2Manufacturing precision
If additional resonators and inductors are added to create resonance circuits for forming attenuation poles, then the steepness of attenuation characteristic is improved, but the device complexity increases
Solution Approach 1:
The series arm resonator and inductor are combined to form a second resonance circuit that produces a sub-resonant frequency. This merging of components creates the necessary attenuation characteristics while minimizing the total number of discrete elements. The parallel arm resonator is strategically placed to provide the primary attenuation pole, and the combined series circuit enhances this effect rather than adding independent redundant components.
Solution Approach 2:
The resonant frequency of the parallel arm resonator and the sub-resonant frequency of the series arm resonator-inductor circuit are carefully selected and tuned to specific parameter values. By optimizing these frequency parameters, the filter achieves steep attenuation characteristics without requiring excessive components. The parameter optimization allows existing components to work at maximum efficiency, reducing the need for additional elements.
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 filter device achieves a steeper attenuation characteristic at the high frequency end of the stop band and reduces insertion loss at the low frequency end of the pass band, enhancing the overall frequency selectivity.
Implementation Method 1
the first parallel arm resonator constitutes a first resonance circuit having a resonant frequency at which an attenuation pole corresponding to a high frequency end of the first stop band is formed
Implementation Method 2
the series arm resonator and the first inductor constitute a second resonance circuit having an anti-resonant frequency on a lower frequency side than the first pass band and having a sub-resonant frequency higher than a resonant frequency of the first resonance circuit
Data Source
AI summary
A filter device having a pass band and a stop band on a lower frequency side than the pass band includes a filter having a pass band including the pass band, a series arm resonator connected in series to the filter, a first inductor directly connected in series to the series arm resonator, and a parallel arm resonator connected between a node on a path connecting the filter and the series arm resonator and the ground. The parallel arm resonator constitutes a resonance circuit having a resonant frequency at which an attenuation pole corresponding to a high frequency end of the first stop band, and the series arm resonator and the inductor constitute a resonance circuit having an anti-resonant frequency on a lower frequency side than the pass band and having a sub-resonant frequency higher than a resonant frequency of the resonance circuit.