RF Filter Bandwidth Ratio Optimization for High Frequency Loss
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Solution Overview
Problem
Existing radio-frequency filters in mobile communication devices face challenges in adjusting pass band widths and sharpness, leading to degraded performance at low frequencies and increased insertion loss at high frequencies due to the frequency difference between series and parallel arm resonators.
Innovation Solution
A filter apparatus with a series arm resonant circuit and a parallel arm resonant circuit, where the series arm resonator has a wider band width ratio than the parallel arm resonator, and a capacitor is connected to the series arm resonator, ensuring sharpness at both ends of the pass band and reducing return loss at high frequencies by improving the Q value of the capacitance component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If acoustic wave resonators are used in a filter with lower pass band frequency in a multiplexer, then the filter structure is simplified, but return loss is degraded at the high frequency side which increases insertion loss of filters with higher pass band frequency
Solution Approach 1:
The patent changes the band width ratio parameter of the series arm resonator to be larger than that of the parallel arm resonator. This parameter optimization improves the Q value of the capacitance component at high frequencies, thereby reducing return loss and insertion loss without changing the acoustic wave resonator structure
Solution Approach 2:
The patent introduces a capacitor connected to the series arm resonator, creating a dynamic resonant circuit that can adjust its characteristics. This allows the filter to maintain good performance across different frequency bands by optimizing the resonant circuit's Q value dynamically
2Manufacturing precision
If the band width ratio of the series arm resonator is made larger than that of the parallel arm resonator, then sharpness at both ends of the pass band is ensured, but the Q value of the capacitance component at high frequency side needs to be improved
Solution Approach 1:
The patent optimizes the band width ratio parameter of the series arm resonator to be larger than that of the parallel arm resonator. This parameter change simultaneously improves sharpness at both pass band ends and, when combined with the capacitor, improves the Q value at high frequencies
Solution Approach 2:
The patent introduces a capacitor as an intermediary element connected to the series arm resonator. This capacitor works together with the resonator to improve the Q value of the capacitance component at high frequencies, acting as a mediator between the resonator and the high-frequency signal
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 ensures high sharpness between the pass band and attenuation band at both frequency ends, reduces return loss at high frequencies, and minimizes insertion loss, while also allowing for size reduction and cost optimization of the filter apparatus.
Implementation Method 1
When the acoustic wave resonators are applied to a filter having a lower pass band frequency in a multiplexer in which multiple filters having different pass band frequencies are connected with a common terminal
Implementation Method 2
Japanese Unexamined Patent Application Publication No. 2005-260909 discloses a configuration of a surface acoustic wave device that defines a band pass filter
Implementation Method 3
a first capacitor connected to the first series arm resonator... improving the Q value of the capacitance component of the series arm resonant circuit at the high frequency side of the anti-resonant frequency
Data Source
AI summary
A filter includes a series arm resonant circuit connected between input/output terminals, and a parallel arm resonant circuit connected between a node on a path connecting the input/output terminals and ground. The series arm resonant circuit includes a series arm resonator having a band width ratio wider than the band width ratio of the parallel arm resonant circuit and a capacitor connected to the series arm resonator.