Acoustic Wave Filter Layout for Low-Loss Duplexer Isolation
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Solution Overview
Problem
Existing acoustic wave filter devices with balanced-unbalanced conversion function face challenges in reducing insertion loss within the pass band while maintaining sufficient attenuation in the attenuation band near the pass band, particularly in duplexer applications for mobile communication systems.
Innovation Solution
The proposed acoustic wave filter device incorporates parallel resonators connected in parallel to longitudinally coupled resonator-acoustic wave filters, with differing electrostatic capacitance, to enhance attenuation in the attenuation band and improve isolation characteristics, using a one-stage configuration to minimize insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If multiple longitudinally coupled resonator-acoustic wave filters are cascaded to each other to increase attenuation in the attenuation band, then the amount of attenuation in the attenuation band near the pass band is increased, but the insertion loss within the pass band is increased
Solution Approach 1:
The invention divides the filter system into two functional parts: a longitudinally coupled resonator-acoustic wave filter for providing balanced-unbalanced conversion and basic filtering, and separate parallel resonators connected to balanced terminals for enhancing attenuation. This segmentation allows each component to be optimized independently, avoiding the need to cascade multiple longitudinally coupled resonator filters which would increase insertion loss.
Solution Approach 2:
The parallel resonators act as intermediary elements that enhance attenuation in the attenuation band without being part of the main signal path through the longitudinally coupled resonator. By connecting these parallel resonators to the balanced terminals, the invention introduces additional attenuation mechanisms that do not interfere with the pass band signal transmission, thus improving attenuation without increasing insertion loss.
2Loss of energy
If a one-stage acoustic wave filter device is used to decrease insertion loss within the pass band, then the insertion loss is reduced, but it is difficult to ensure a larger amount of attenuation in the attenuation band near the pass band
Solution Approach 1:
The invention merges two different filter configurations into a single device: the longitudinally coupled resonator-acoustic wave filter structure provides balanced-unbalanced conversion and pass band characteristics, while parallel resonators connected to balanced terminals provide enhanced attenuation in the attenuation band. This combination allows the device to achieve both low insertion loss and high attenuation performance simultaneously.
Solution Approach 2:
The acoustic wave filter device performs multiple functions: it provides balanced-unbalanced conversion through the longitudinally coupled resonator, maintains low insertion loss through the one-stage configuration, and achieves high attenuation in the attenuation band through the added parallel resonators. This multi-functionality allows a single device to meet multiple performance requirements that would otherwise require separate components.
3Device complexity
If parallel resonators with the same electrostatic capacitance are connected to both balanced terminals, then the circuit is symmetric, but the isolation characteristics in duplexer applications are degraded
Solution Approach 1:
The invention introduces asymmetry by setting different electrostatic capacitance values for the first and second parallel resonators. The first parallel resonator has a different electrostatic capacitance than the second parallel resonator, which breaks the circuit symmetry but significantly improves isolation characteristics in duplexer applications. This asymmetry allows better differentiation between transmission and reception signals, enhancing the overall performance of the duplexer system.
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 configuration effectively increases attenuation in the attenuation band near the pass band and improves isolation characteristics, while maintaining low insertion loss and sharpness of filter characteristics, specifically in duplexer applications.
Implementation Method 1
A longitudinally coupled resonator-surface acoustic wave filter device includes an unbalanced terminal; first and second balanced terminals; longitudinally coupled resonator-surface acoustic wave filters that are connected between the unbalanced terminal and the first balanced terminal and between the unbalanced terminal and the second balanced terminal
Implementation Method 2
The resonant frequency of the series resonator 607 is positioned within the pass band of the reception filter and the anti-resonant frequency of the series resonator 607 is positioned within an attenuation band at a higher side of the pass band of the reception filter
Data Source
AI summary
An acoustic wave filter device includes longitudinally coupled resonator-acoustic wave filters having a balanced-unbalanced conversion function, and increases the amount of attenuation in an attenuation band and improves the isolation characteristics when the acoustic wave filter device is used as a reception filter of a duplexer. The acoustic wave filter device includes an unbalanced terminal, first and second balanced terminals, first and second longitudinally coupled resonator-acoustic wave filters that are connected between the unbalanced terminal and the first balanced terminal and between the unbalanced terminal and the second balanced terminal, respectively, a first parallel resonator connected between the first balanced terminal and a ground potential, and a second parallel resonator connected between the second balanced terminal and the ground potential. The electrostatic capacitance of the first parallel resonator is different from the electrostatic capacitance of the second parallel resonator. Among the first parallel resonator and the second parallel resonator, the wavelength of the first parallel resonator having a relatively small electrostatic capacitance is shorter than the wavelength of the second parallel resonator having a relatively large electrostatic capacitance.