Composite Acoustic Filter Layout for Close Pass-Band Isolation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing composite filter devices face challenges in achieving both excellent bandpass characteristics and isolation characteristics when the pass bands of bandpass filters are close to each other, often resulting in deteriorated bandpass characteristics in the target pass band.
Innovation Solution
A composite filter device is designed with a first acoustic wave filter and a second acoustic wave filter, where the second filter is a ladder filter with specific resonant and anti-resonant frequency relationships between its parallel arm resonators, reducing insertion loss and improving isolation characteristics by optimizing the resonant frequencies and capacitance of the parallel arm resonators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If bandpass filters are connected in common to achieve multiplexing, then isolation characteristics improve, but bandpass characteristics in the target pass band deteriorate when pass bands are close to each other
Solution Approach 1:
The patent applies parameter changes by optimizing the resonant frequencies and electrostatic capacitances of the parallel arm resonators in the ladder filter. Specifically, it sets the resonant frequency of each parallel arm resonator to be lower than the anti-resonant frequency of adjacent series arm resonators, and adjusts the electrostatic capacitance values to achieve proper impedance matching. These parameter optimizations enable the filter to maintain both excellent isolation characteristics and bandpass characteristics when pass bands are close together.
2Object-generated harmful factors
If isolation characteristics are improved in composite filter devices, then attenuation in non-target pass bands increases, but insertion loss in the target pass band increases
Solution Approach 1:
The patent resolves this contradiction through precise parameter optimization of the parallel arm resonators. By setting specific resonant frequencies below the anti-resonant frequencies of adjacent series arm resonators and optimizing electrostatic capacitance values, the filter achieves proper impedance matching and signal transmission efficiency. This enables strong attenuation in non-target pass bands while maintaining low insertion loss in the target pass band.
Solution Approach 2:
The patent employs dynamic design in the ladder filter structure where parallel arm resonators are strategically positioned and tuned to create frequency-dependent behavior. The resonators dynamically respond to different frequency signals, providing high attenuation for frequencies outside the pass band while maintaining low insertion loss for frequencies within the pass band through controlled resonance and anti-resonance effects.
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 significantly reduces insertion loss and enhances isolation characteristics in the pass band, providing improved filter performance compared to comparative examples.
Implementation Method 1
a second acoustic wave filter having a second pass band higher than the first pass band. One end of the first acoustic wave filter and one end of the second acoustic wave filter are connected in common by a common terminal. The second acoustic wave filter is a ladder filter including a plurality of parallel arm resonators defined by acoustic wave resonators.
Data Source
AI summary
A composite filter device includes a transmission filter and a reception filter first and second acoustic wave filters, respectively. The first acoustic wave filter has a first pass band and the second acoustic wave filter has a second pass band higher than the first pass band. One end of the first acoustic wave filter and one end of the second acoustic wave filter are connected in common by a common terminal. The second acoustic wave filter is a ladder filter including parallel arm resonators defined by acoustic wave resonators. The inequalities of fq<fr and fr<fp<fa are satisfied, where fq and fp represent a resonant frequency and an anti-resonant frequency, respectively, of one of the parallel arm resonators having the lowest capacitance and fr and fa represent resonant frequencies and anti-resonant frequencies, respectively, of other ones of the parallel arm resonators.