Multiplexer Filter Layout for Adjacent-Band Isolation
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Solution Overview
Problem
In multiplexers used in mobile terminals for multiband communications, the isolation characteristics between filters passing adjacent frequency bands are compromised due to magnetic field coupling between inductors forming attenuation poles, leading to insufficient attenuation and deteriorated isolation performance.
Innovation Solution
The placement of components from another filter between inductors forming attenuation poles in adjacent filters reduces magnetic field coupling, thereby enhancing the isolation characteristics between filters passing adjacent frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If inductors forming attenuation poles are placed close to each other in adjacent filters, then device complexity is reduced, but magnetic field coupling causes signal leakage and deteriorates isolation characteristics
Solution Approach 1:
A ground electrode is introduced as an intermediary element between the first inductor and the second inductor. This ground electrode acts as a magnetic field shield, blocking the magnetic coupling between the two inductors and preventing signal leakage, thereby improving isolation characteristics while maintaining the compact filter configuration
Solution Approach 2:
The harmful magnetic field coupling effect is extracted and blocked by introducing a separate ground electrode element. This ground electrode is specifically positioned to intercept and shield the magnetic field paths between inductors, separating the harmful electromagnetic interaction from the functional signal paths
2Reliability
If ground electrodes are added between inductors to reduce magnetic coupling, then isolation characteristics improve, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The ground electrode serves multiple functions simultaneously: it acts as a magnetic field shield between inductors, provides a reference potential plane, and serves as part of the overall ground structure of the multiplexer. This multi-functionality reduces the need for additional separate elements, simplifying manufacturing despite the added shielding function
3Loss of energy
If inductors are positioned closer together, then insertion loss is reduced, but magnetic field coupling increases causing insufficient attenuation at band boundaries
Solution Approach 1:
The ground electrode is positioned between the inductors to act as a magnetic field barrier. This allows the inductors to be placed closer together for lower insertion loss while the ground electrode prevents magnetic field coupling and signal leakage, achieving both low loss and sharp attenuation at band boundaries
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 the isolation characteristics between filters, increasing the sharpness of attenuation at band boundaries and reducing signal leakage, while maintaining low insertion loss and allowing for a wider frequency band coverage.
Implementation Method 1
inductors that form attenuation poles couple to each other via a magnetic field
Data Source
AI summary
A multiplexer (100) includes a first filter (FLT1) that passes a signal in a first frequency band, a second filter (FLT2) that passes a signal in a second frequency band lower than the first frequency band, and a third filter (FLT3) that passes a signal in a third frequency band. The third frequency band is a frequency band higher than the first frequency band, or a frequency band lower than the second frequency band. The first filter includes a first inductor (L11) that forms a first attenuation pole on a low-frequency side of the first frequency band. The second filter includes a second inductor (L23) that forms a second attenuation pole on a high-frequency side of the second frequency band. At least a portion of a component constituting the third filter is disposed between the first inductor and the second inductor.