Ladder Filter Capacitance Layout for Narrow Pass Band Control
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Solution Overview
Problem
Existing ladder filters face issues with pass band widening and deteriorated reflection characteristics due to mismatched resonant and anti-resonant frequencies of serial and parallel arm resonators, leading to inadequate attenuation near the pass band.
Innovation Solution
The ladder filter design incorporates serial and parallel arm resonators with wider frequency intervals and additional capacitances in specific arms, setting resonant frequencies of serial arm resonators lower and anti-resonant frequencies of parallel arm resonators higher than the relevant band, while replacing some resonators with capacitances to achieve neutral impedance characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the resonant frequency of parallel arm resonators is matched with the resonant frequency of serial arm resonators to ensure attenuation near the pass band, then the attenuation characteristic is improved, but the pass band becomes excessively wider than the relevant band
Solution Approach 1:
The patent changes the frequency parameters of the resonators by setting the resonant frequency of serial arm resonators lower than the relevant band and the anti-resonant frequency of parallel arm resonators higher than the relevant band. This parameter adjustment narrows the pass band to match the relevant band while maintaining adequate attenuation through the frequency interval between resonant and anti-resonant frequencies.
2Reliability
If the resonant frequency of parallel arm resonator is set high and the resonant frequency of serial arm resonator is set low to ensure attenuation near the pass band, then the attenuation characteristic is improved, but the impedance characteristics of the pass band become inductive, causing the reflection characteristic to deteriorate
Solution Approach 1:
The patent introduces capacitances as intermediary elements connected to specific nodes in the ladder filter structure. These capacitances act as mediators that adjust the impedance characteristics of the pass band from inductive to neutral, thereby improving reflection characteristics while preserving the attenuation performance achieved through the resonator frequency configuration.
Data Source
AI summary
A ladder filter includes serial arm resonators in a serial arm and parallel arm resonators in parallel arms. A resonant frequency of at least one of the serial arm resonators is lower than a relevant band. An anti-resonant frequency of at least one of the parallel arm resonators is higher than the relevant band. The ladder filter includes one or more capacitances provided in at least one of the serial arm and the parallel arms. The capacitances are not provided in one or more of the parallel arms in which the one or more parallel arm resonators are provided.