Duplexer Branching Circuit With Inductive Coupling for Filter Isolation
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Solution Overview
Problem
Existing branching devices in communication devices, such as cellular phones, face challenges in reducing device size while maintaining signal separation and isolation characteristics between filters with different pass bands, leading to inadequate attenuation and isolation of signals outside target bands.
Innovation Solution
A branching device configuration that includes multiple signal terminals, filters, and inductors, where inductors are strategically positioned and coupled to enhance impedance matching and inductive coupling, thereby increasing attenuation and isolation characteristics by adjusting the coupling coefficient and distances between inductors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple filters are used to separate signals of different pass bands, then signal separation capability is improved, but device size increases and isolation characteristics between filters deteriorate
Solution Approach 1:
The patent combines multiple filters and inductors into a single integrated branching device structure. The first and second filters are arranged to share common signal terminals and ground connections, while the inductors are positioned to provide impedance matching for multiple filters simultaneously. This merging approach achieves signal separation for multiple pass bands while maintaining a compact form factor that would be smaller than separate filter assemblies.
2Volume of stationary object
If filters are placed closer together to reduce device size, then device size is reduced, but isolation characteristics between filters deteriorate
Solution Approach 1:
The patent introduces inductors as intermediary elements between the signal terminals and the filters. These inductors serve dual purposes: they provide impedance matching for the filters while also acting as isolation elements that reduce electromagnetic coupling between adjacent filters. By positioning inductors strategically between filters and adjusting their inductance values, the design achieves both compact spacing and adequate isolation characteristics.
3Reliability
If inductors are added to improve impedance matching and isolation, then isolation characteristics are improved, but device complexity increases
Solution Approach 1:
The inductors in the patent are designed to perform multiple functions simultaneously. Each inductor provides impedance matching for its associated filter while also contributing to the isolation between adjacent filters. Additionally, the inductors are positioned to create controlled inductive coupling that enhances attenuation outside pass bands. This multi-functionality reduces the need for separate isolation components, thereby limiting the increase in device complexity despite the addition of inductors.
4Reliability
If inductive coupling between inductors is increased to improve attenuation, then attenuation outside pass bands is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent controls the inductive coupling between inductors by adjusting the inductance values and physical spacing parameters within a specific range. By optimizing these parameters during the design phase, the patent achieves adequate attenuation outside pass bands while maintaining tolerance ranges that are feasible for standard manufacturing processes. The coupling coefficient is controlled through parameter optimization rather than requiring extremely precise positioning, thus balancing attenuation performance with manufacturing precision requirements.
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
The configuration effectively increases attenuation outside pass bands and improves isolation between filters, enhancing signal separation and reducing interference, even in compact device designs.
Implementation Method 1
The first inductor inductively couples with the second inductor and the third inductor
Data Source
AI summary
A branching device that separates signals of different pass bands increases attenuation characteristics outside the pass bands, and increases isolation characteristics. The branching device includes a duplexer including a transmission filter and a reception filter electrically connected to an antenna terminal, and a filter electrically connected to the antenna terminal. An inductor is electrically connected between the antenna terminal and a ground potential. The transmission filter is a ladder filter including serial arm resonators and parallel arm resonators, and each includes a polarized inductor electrically connected between the parallel arm resonators and a ground potential. The inductor and the polarized inductors inductively couple with each other, and a distance between the inductor and the polarized inductors is shorter than a distance between the polarized inductors.