RF Filter Circuit Using Parallel Resonators for Wider Low-Side Attenuation
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Solution Overview
Problem
Existing radio-frequency filter circuits struggle to increase the bandwidth of the attenuation band on the low band side of the pass band, as they typically have only one parallel arm resonator forming an attenuation pole, limiting the width of the attenuation band on this side.
Innovation Solution
A radio-frequency filter circuit design that includes a series-arm circuit and a parallel-arm circuit, where one circuit is formed by a first and a second resonator connected in parallel, with the second resonator having a lower resonant frequency and higher impedance than the first, allowing for the formation of an attenuation pole at a lower frequency while maintaining low insertion loss at the higher end of the pass band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If only one parallel-arm resonator is used to form an attenuation pole, then the device complexity is reduced, but the bandwidth of the attenuation band on the low band side cannot be increased
Solution Approach 1:
The parallel-arm circuit is segmented into multiple resonators (first parallel-arm resonator and second parallel-arm resonator) with different resonant frequencies. Each resonator contributes to forming attenuation poles at different frequency positions, thereby expanding the overall attenuation bandwidth on the low band side without requiring a single complex resonator structure
Solution Approach 2:
The resonant frequencies of the parallel-arm resonators are strategically designed with specific frequency relationships (second resonator's resonant frequency is higher than the first resonator's resonant frequency by a predetermined ratio). By changing and optimizing these frequency parameters, the attenuation band bandwidth is increased while maintaining controlled device complexity
2Quantity of substance
If a second resonator with lower resonant frequency is added to increase attenuation band bandwidth, then the bandwidth of attenuation band on low band side is increased, but insertion loss at higher end of pass band may increase
Solution Approach 1:
Different resonators are assigned specific local functions within the frequency spectrum. The first parallel-arm resonator primarily handles attenuation in one frequency region, while the second parallel-arm resonator addresses attenuation in another frequency region. This localized functional assignment allows each resonator to optimize its performance for specific frequency ranges, increasing attenuation bandwidth while controlling insertion loss in the pass band
Solution Approach 2:
The parallel-arm resonators are designed with asymmetric resonant frequency relationships rather than uniform spacing. The second resonator's resonant frequency is set to be higher than the first resonator's resonant frequency by a predetermined ratio, creating an asymmetric frequency distribution that effectively expands the attenuation band while maintaining favorable insertion loss characteristics
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 design effectively increases the bandwidth of the attenuation band on the low band side while suppressing insertion loss, enhancing the steepness and attenuation characteristics of the filter.
Implementation Method 1
an elastic wave filter using an elastic wave has been widely used for a bandpass filter or the like disposed at a front-end portion of a mobile communication apparatus
Data Source
AI summary
A filter (11) includes a series-arm circuit (10) connected between an input/output terminal (11m) and an input/output terminal (11n); and a parallel-arm circuit (20) connected between a ground and a path that connects the input/output terminal (11m) and the input/output terminal (11n). One circuit among the series-arm circuit (10) and the parallel-arm circuit (20) is constituted by a parallel-arm resonator (p1) and a parallel-arm resonator (p2) that are connected in parallel to each other and that are connected to a node (x1) on the path. The parallel-arm resonators (p1) and (p2) form a pass band, together with another circuit among the series-arm circuit (10) and the parallel-arm circuit (20). The parallel-arm resonator (p2) has a resonant frequency lower than a resonant frequency of the parallel-arm resonator (p1) and has an impedance higher than an impedance of the parallel-arm resonator (p1).