Antenna Multiplexer Capacitance Layout for Better Filter Isolation
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Solution Overview
Problem
Existing multiplexers in mobile communication devices face challenges in achieving improved isolation characteristics between filters, particularly in multiband communications, where accurate separation of signals with different pass bands and reduced attenuation outside the pass band are necessary.
Innovation Solution
A multiplexer configuration that includes an antenna terminal, an inductance element, and first and second acoustic wave filters, where the second filter has a higher center frequency and larger electrostatic capacitance in its parallel arm resonance portions closest to the antenna terminal, ensuring improved isolation and impedance matching between the transmission-side and reception-side filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional multiplexer configuration with filters connected to a common antenna terminal is used, then the device achieves basic signal separation functionality, but the isolation characteristics between filters are insufficient
Solution Approach 1:
The patent applies local quality by making the first parallel arm resonance portion have different electrostatic capacitance characteristics compared to other parallel arm resonance portions. Specifically, the first parallel arm resonance portion is configured with electrostatic capacitance that satisfies a particular inequality relationship, creating localized electrical property differences that improve signal attenuation in specific frequency regions while maintaining passband characteristics.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the electrostatic capacitance values of the parallel arm resonance portions to specific ranges. The first parallel arm resonance portion is designed with electrostatic capacitance C1 satisfying 0.05pF < C1 < 0.20pF, while other parallel arm resonance portions have electrostatic capacitance C2 satisfying 0.05pF < C2 < 0.15pF. This parameter optimization enables improved isolation characteristics without significantly increasing insertion loss.
2Reliability
If the electrostatic capacitance of parallel arm resonance portions is increased to improve isolation, then the isolation characteristics improve, but the insertion loss increases
Solution Approach 1:
The patent resolves this contradiction through precise parameter optimization. By setting the electrostatic capacitance of the first parallel arm resonance portion to 0.05pF < C1 < 0.20pF and other parallel arm resonance portions to 0.05pF < C2 < 0.15pF, the design achieves improved isolation characteristics while controlling insertion loss within acceptable ranges. This optimized parameter selection prevents excessive energy loss while maintaining effective signal separation.
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 enhances the isolation characteristics between filters while maintaining low insertion loss, effectively separating signals across different pass bands and reducing attenuation in the desired frequency ranges, particularly beneficial in multiband communications.
Implementation Method 1
a low pass filter for impedance matching is disposed between a common connection point of both of the transmission-side surface acoustic wave filter and the reception-side surface acoustic wave filter and the antenna terminal
Implementation Method 2
a low pass filter for impedance matching is disposed between a common connection point
Implementation Method 3
a transmission-side surface acoustic wave filter and a reception-side surface acoustic wave filter are connected to a common antenna terminal
Implementation Method 4
a separation device (multiplexer) for separating a transmission signal and a reception signal according to frequency by using a plurality of filters corresponding to the respective frequency bands
Implementation Method 5
Electrostatic capacitance of the first parallel arm resonance portion is larger than electrostatic capacitance of any other parallel arm resonance portions of the plurality of parallel arm resonance portions
Implementation Method 6
a plurality of parallel arm resonance portions including a first parallel arm resonance portion connected closest to the inductance element
Data Source
AI summary
A multiplexer includes an antenna terminal, an inductance element, and a transmission-side filter and a reception-side filter connected to the antenna terminal. The transmission-side filter has a first pass band, and the reception-side filter has a second pass band. The reception-side filter is connected to the antenna terminal through the inductance element. A center frequency of the second pass band is higher than a center frequency of the first pass band. The reception-side filter includes parallel arm resonance portions including a first parallel arm resonance portion connected closest to the inductance element. An electrostatic capacitance of the first parallel arm resonance portion is larger than an electrostatic capacitance of any other parallel arm resonance portions.