Elastic Wave Duplexer Layout for Balanced Terminal Capacitance
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Solution Overview
Problem
In elastic wave apparatuses, particularly in surface acoustic wave filters used as bandpass filters in RF stages of mobile telephones, it is challenging to maintain signal balance between first and second balanced terminals while reducing the size of the package, as it becomes difficult to freely dispose electrodes and lines, leading to deterioration in balance and insufficient capacitance.
Innovation Solution
The elastic wave apparatus includes a longitudinally coupled resonator-type filter element with unbalanced, first balanced, and second balanced terminals on a multilayer wiring board, where internal lines with different lengths or shapes are strategically positioned to generate capacitance between them, ensuring the same current direction, thereby improving signal balance without increasing the thickness of the board.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the package size is reduced, then the size of the elastic wave apparatus is decreased, but it becomes difficult to freely dispose electrodes and lines, leading to deterioration in signal balance and insufficient capacitance
Solution Approach 1:
The patent utilizes the thickness dimension of the multilayer wiring board to route internal lines between balanced terminals. By forming capacitor electrodes on different layers (first capacitor electrode on one layer, second capacitor electrode on another layer) and connecting them via via holes, the invention creates capacitance in the vertical dimension rather than requiring horizontal spacing. This allows signal balance correction while maintaining a compact planar footprint.
Solution Approach 2:
The invention combines multiple functions into the internal lines and capacitor structures: the internal lines serve both as signal transmission paths and as one electrode of the capacitor, while the capacitor electrodes are integrated into the wiring board layers themselves. This merging of transmission and capacitance functions into unified structures achieves both signal balance correction and size reduction.
2Volume of moving object
If the package size is reduced, then the size of the elastic wave apparatus is decreased, but sufficient capacitance cannot be obtained to improve balance between balanced terminals
Solution Approach 1:
The patent generates capacitance in the vertical dimension by placing capacitor electrodes on different layers of the multilayer wiring board. The first capacitor electrode is formed on one layer and the second capacitor electrode on another layer, with via holes providing electrical connection between layers. This three-dimensional arrangement creates sufficient capacitance without requiring large horizontal area, thus achieving size reduction while maintaining adequate capacitance for balance correction.
Solution Approach 2:
The invention creates a capacitance effect by forming two capacitor electrodes (first and second capacitor electrodes) that replicate the functional role of a traditional external capacitor. These electrodes are positioned to generate the necessary capacitance between balanced terminals, effectively copying the function of an external capacitor element while integrating it into the compact multilayer structure.
3Reliability
If external capacitor elements are used to correct frequency characteristic differences, then amplitude and phase balance can be improved, but the device size increases
Solution Approach 1:
The invention merges the capacitor function with the existing multilayer wiring board structure. The capacitor electrodes are formed on the wiring board layers themselves, and the capacitance is generated within the board rather than requiring separate external capacitor components. This integration eliminates the need for additional external capacitor elements, achieving balance correction without increasing device size.
Solution Approach 2:
The multilayer wiring board serves multiple functions: it provides mechanical support, routes signal lines between terminals, and generates capacitance for balance correction. The internal lines serve both as transmission paths and as capacitor electrodes. This multi-functionality eliminates the need for separate dedicated capacitor components, achieving both size reduction and balance improvement.
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 effectively prevents the deterioration of signal balance between the first and second balanced terminals, achieving improved balance and size reduction while maintaining the balanced-unbalanced transforming function, even in reduced-size designs.
Implementation Method 1
a capacitance is generated in an adjacent area where portions of the first and second internal lines are adjacent to each other
Implementation Method 2
surface acoustic wave filters have been recently used as, for example, bandpass filters in RF stages of mobile telephones
Implementation Method 3
A surface acoustic wave apparatus 1001 is obtained by forming illustrated electrodes on a piezoelectric substrate
Data Source
AI summary
An elastic wave apparatus includes a balanced-unbalanced transforming function, and an elastic wave filter and a multilayer wiring board on which the elastic wave filter is mounted. The elastic wave filter includes an unbalanced terminal and first and second balanced terminals. External electrodes used are provided on the multilayer wiring board. A first internal line connects the first balanced terminal and the external electrode. A second internal line connects the second balanced terminal and the external electrode. The lengths or shapes of the first internal line and the second internal line are set so that a capacitance used for the improvement of a balance is generated in an adjacent area A where the first internal line and the second internal line are adjacent to each other. In the adjacent area A, the directions of currents passing through the first internal line and the second internal line are the same.