External Inductor Placement in Duplexers for Isolation and Size
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Solution Overview
Problem
The miniaturization of duplexers with ladder elastic wave filters is hindered by the need for large spaces to accommodate electromagnetic coupling devices, which limits their application in compact devices like cellular phones.
Innovation Solution
The duplexer design includes an inductance component positioned outside the piezoelectric substrate, with its longitudinal direction parallel to one side of the substrate, and a coil winding perpendicular to the mounting surface, enhancing electromagnetic coupling and allowing for miniaturization without increasing the physical size of the module substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electromagnetic coupling device includes a plurality of coiled patterns connected by via-hole electrodes, then electromagnetic coupling is achieved, but a large space is required in the piezoelectric substrate making miniaturization difficult
Solution Approach 1:
The inductance component is extracted from the piezoelectric substrate and mounted externally on the module substrate. This separates the electromagnetic coupling function from the substrate interior, eliminating the need for via-hole electrodes and coiled patterns within the substrate, thereby achieving miniaturization while maintaining coupling effectiveness
Solution Approach 2:
The inductance component is positioned in a different spatial dimension (outside the substrate plane) rather than being embedded within the substrate. The longitudinal direction of the inductance component extends parallel to one side of the substrate, utilizing external space to achieve electromagnetic coupling without consuming substrate area
2Area of stationary object
If the inductance component is disposed outside the piezoelectric substrate with longitudinal direction parallel to one side, then miniaturization is achieved, but electromagnetic coupling effectiveness may be compromised
Solution Approach 1:
The inductance component is strategically positioned adjacent to one side of the piezoelectric substrate where electromagnetic coupling is most effective. The longitudinal direction is oriented parallel to the substrate side to maximize coupling with the transmitting filter's elastic wave resonators, ensuring reliable electromagnetic coupling despite the external placement
Solution Approach 2:
The inductance component serves as an external intermediary element that mediates electromagnetic coupling between the transmitting filter and the antenna terminal. By positioning it outside the substrate with proper orientation, it effectively couples electromagnetic energy without requiring internal substrate modifications
3Reliability
If the inductance component includes a coil winding with axial direction perpendicular to mounting surface, then electromagnetic coupling is improved, but device complexity increases
Solution Approach 1:
The coil winding's axial direction is changed to be perpendicular to the mounting surface, which optimizes the electromagnetic coupling characteristics and improves isolation in the receiving filter pass band. This parameter change enhances performance while the coil winding itself remains a standard inductance component structure
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 improves isolation characteristics in the pass band of the receiving filter and achieves further miniaturization of the duplexer, enabling effective electromagnetic coupling with reduced space requirements.
Implementation Method 1
an inductance component connected at one end to the antenna terminal, and connected at another end to a ground potential. The inductance component is disposed outside the piezoelectric substrate and is mounted on the module substrate
Implementation Method 2
a transmitting filter connected between the antenna terminal and the transmitting terminal and including at least one elastic wave filter including a piezoelectric substrate that is mounted on the module substrate
Data Source
AI summary
A duplexer includes elastic wave resonators disposed on a piezoelectric substrate to define a ladder elastic wave filter including shunt-arm resonators and series-arm resonators. The duplexer includes an inductance component connected between an antenna terminal and a ground potential. A transmitting filter includes the ladder elastic wave filter. The inductance component is disposed outside a short side of the piezoelectric substrate such that the electromagnetic coupling between the shunt-arm resonator located closest to a transmitting terminal in the ladder circuit configuration, and the inductance component is stronger than the electromagnetic coupling between the inductance component and the remaining shunt-arm resonators.