RF Ladder Filter Resonator Tuning for Spurious Resonance Suppression
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Solution Overview
Problem
Existing radio frequency filters with series and parallel resonators suffer from spurious resonance at frequencies different from the resonant frequency, leading to insufficient attenuation outside the pass band, which affects the performance of multiplexers used in communication devices.
Innovation Solution
A filter design incorporating a specific configuration of series and parallel resonators with strategically placed inductors and electrode pitch adjustments, where the first and third series resonators have higher resonant frequencies than the second, and smaller capacitances, to widen the pass band and reduce spurious resonance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If an inductor is connected in parallel to the parallel resonator to widen the pass band width, then the pass band width is widened, but spurious resonance is generated at frequencies different from the resonant frequency
Solution Approach 1:
The harmful inductor component is extracted and removed from the circuit configuration. Instead of connecting inductors in parallel with parallel resonators, the patent uses only series resonators and parallel resonators without additional inductor components, thereby eliminating the source of spurious resonance while maintaining pass band width through optimized resonator parameters and configuration
Solution Approach 2:
The patent changes the parameters of the resonators themselves to achieve pass band widening without introducing harmful inductors. By adjusting the resonant frequencies and impedance values of the series and parallel resonators, the pass band width is widened while avoiding spurious resonance through proper parameter selection
2Length of moving object
If an inductor is connected in parallel to the parallel resonator, then the pass band width is widened, but attenuation outside the pass band becomes insufficient
Solution Approach 1:
The inductor component that causes insufficient attenuation is extracted and removed. The patent achieves both pass band width and attenuation performance by using optimized resonator configurations without additional inductor components
Solution Approach 2:
The resonator parameters are optimized to simultaneously achieve wide pass band and high attenuation. By carefully selecting the resonant frequencies and impedance values of series and parallel resonators, the filter achieves both widening of pass band and sufficient attenuation outside the pass band
3Length of moving object
If the resonant frequencies of series resonators are made higher than parallel resonators, then pass band width is widened, but spurious resonance affects other filters in the multiplexer
Solution Approach 1:
The patent optimizes the resonant frequency parameters to eliminate spurious resonance while maintaining wide pass band. By setting appropriate resonant frequency relationships between series and parallel resonators, the design achieves pass band width without generating harmful spurious resonance that would affect other filters
Solution Approach 2:
The patent converts the potential harmful effect of resonance interactions into a benefit by carefully designing the resonant frequency relationships. The resonance characteristics are utilized constructively to achieve wide pass band while the spurious resonance is suppressed through proper parameter selection, turning a potential problem into a solution
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 proposed filter design effectively widens the pass band, reduces spurious resonance, and increases attenuation outside the pass band, improving the performance of multiplexers by minimizing insertion loss and impedance mismatch.
Implementation Method 1
a phenomenon that a resonance (hereinafter also called a 'spurious resonance' in some cases) at a frequency different from a resonant frequency is generated by an L component of the inductor connected in parallel and a C component of the parallel resonator
Implementation Method 2
a ladder filter including a series resonator and a parallel resonator is proposed as a filter for use in the above-mentioned multiplexer
Data Source
AI summary
A filter includes n series resonators, one or more parallel resonators, a first inductor between a first terminal and a first of the n series resonators, and a second inductor between an n-th series resonator and a second terminal. Where a resonant frequency of the first series resonator is referred to as a first resonant frequency, a resonant frequency of each of the series resonators other than the first series resonator and the n-th series resonator is referred to as a second resonant frequency, and a resonant frequency of the n-th series resonator is referred to as a third resonant frequency, the first resonant frequency and the third resonant frequency are each higher than the second resonant frequency.