Branching Filter Layout for Miniaturized Tx-Rx Isolation
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Solution Overview
Problem
Miniaturization of branching filters can deteriorate the isolation characteristic between transmission and reception signal terminals due to changes in the disposition of ladder-type and longitudinally coupled resonator-type elastic wave filters.
Innovation Solution
A branching filter configuration with a ladder-type elastic wave filter unit connected between an antenna and transmission signal terminal and a longitudinally coupled resonator-type elastic wave filter unit between the antenna and reception signal terminals, where the transmission signal propagation direction is perpendicular to reception signal propagation directions, maintaining isolation characteristics through specific electrode and resonator arrangements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the branching filter is miniaturized by changing the disposition of the ladder-type elastic wave filter or longitudinally coupled resonator-type elastic wave filter, then the size of the filter is reduced, but the isolation characteristic between transmission signal terminal and reception signal terminals deteriorates
Solution Approach 1:
The patent applies dimensionality change by making the transmission signal propagation direction perpendicular to the reception signal propagation direction. This spatial arrangement in three-dimensional space allows the filter to maintain isolation characteristics while reducing overall size, as the perpendicular orientation minimizes electromagnetic coupling between transmission and reception paths without requiring excessive separation distance
Solution Approach 2:
The patent employs asymmetry in the disposition of the ladder-type elastic wave filter and longitudinally coupled resonator-type elastic wave filter. The filters are arranged with specific asymmetric positioning where the transmission path and reception path are oriented perpendicular to each other, creating an asymmetric layout that optimizes isolation while enabling compact form factor
2Area of stationary object
If the ladder-type elastic wave filter and longitudinally coupled resonator-type elastic wave filter are disposed closer together for miniaturization, then the device area is reduced, but electromagnetic coupling between transmission and reception paths increases
Solution Approach 1:
The patent utilizes three-dimensional spatial arrangement by orienting the transmission signal propagation direction perpendicular to the reception signal propagation direction. This perpendicular configuration in the third dimension allows compact planar layout while maintaining adequate electromagnetic isolation, as the orthogonal orientations reduce parasitic coupling compared to parallel arrangements
Solution Approach 2:
The patent introduces ground potential connections and specific electrode arrangements as intermediary elements between the ladder-type filter and longitudinally coupled resonator-type filter. These intermediary structures act as electromagnetic shields and reference planes that reduce harmful coupling effects while allowing the filters to be positioned closer together for miniaturization
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 allows for miniaturization while maintaining favorable isolation characteristics between transmission and reception signal terminals, reducing electromagnetic coupling and crosstalk, as demonstrated by improved differential isolation and insertion loss performance.
Implementation Method 1
elastic wave branching filters using elastic waves, such as surface acoustic waves or boundary acoustic waves
Implementation Method 2
ladder-type elastic wave filter unit includes series arm resonators and a parallel arm resonator; longitudinally coupled resonator-type elastic wave filter unit includes first and second functional electrode units
Data Source
AI summary
A branching filter includes a ladder-type elastic wave filter unit connected between an antenna terminal and a transmission signal terminal and a longitudinally coupled resonator-type elastic wave filter unit connected between an antenna terminal and first and second balanced reception signal terminals while maintaining the isolation characteristics between the transmission signal terminal and the first and second reception signal terminals. In a duplexer, a transmission signal propagation direction is perpendicular or substantially perpendicular to each of a first reception signal propagation direction and a second reception signal propagation direction.