Acoustic Wave Filter LC Layout for Isolation and Attenuation
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Solution Overview
Problem
Existing acoustic wave filters, particularly ladder-type filters, face challenges in achieving improved out-of-band attenuation characteristics and isolation in multiplexers used in communication apparatuses.
Innovation Solution
Incorporating a capacitor part and an inductor part connected in series between the ladder-type filter and the signal terminal, forming an LC serial resonance circuit, which enhances attenuation characteristics and reduces insertion losses by positioning these components closer to the signal terminal rather than the antenna terminal, thereby improving impedance matching and heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ladder-type filter is used as a transmission filter in a multiplexer, then the filter can process transmission signals, but the isolation between the transmission filter and receiving filter is insufficient
Solution Approach 1:
The filter is divided into two independent ladder-type filters (transmission filter and receiving filter) with separate signal paths. Each filter operates independently with its own input and output terminals, eliminating signal interference and improving isolation characteristics between transmission and receiving paths.
Solution Approach 2:
A bandpass filter is introduced as an intermediary component connected between the antenna terminal and the receiving filter. This intermediary filter selectively passes only the receiving signal band while blocking transmission signals, thereby enhancing isolation between the transmission and receiving paths.
2Reliability
If the capacitor and inductor are positioned closer to the antenna terminal, then the out-of-band attenuation characteristic improves, but the insertion loss increases
Solution Approach 1:
The capacitance and inductance values are optimized to achieve the desired out-of-band attenuation while minimizing insertion loss. By carefully selecting component parameters, the filter achieves deep attenuation in stopbands while maintaining low insertion loss in the passband.
Solution Approach 2:
The capacitor and inductor are positioned at multiple locations within the filter structure, not just at single points. This distributed placement provides cumulative attenuation effect across different frequency ranges while distributing the insertion loss impact, achieving better overall performance.
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 acoustic wave filter's attenuation characteristics, maintains low insertion losses, and improves isolation in multiplexers, ensuring better performance in communication apparatuses by precisely controlling resonance frequencies and reducing the size of the filter.
Implementation Method 1
An acoustic wave resonator for example includes a piezoelectric substrate and an IDT (interdigitated transducer) electrode positioned on the piezoelectric substrate
Implementation Method 2
The acoustic wave is for example a surface acoustic wave (SAW)
Implementation Method 3
a capacitor part and an inductor part which are connected in series between a position between the ladder-type filter and the first signal terminal and a reference potential
Data Source
AI summary
An acoustic wave filter includes a first signal terminal, an antenna terminal, a ladder-type filter connected between the first signal terminal and the antenna terminal and including one or more serial resonators and one or more parallel resonators connected in a ladder shape, and a capacitor part and an inductor part which are connected in series between the first signal terminal and a reference potential.