Multilayer LC Stub Filter Layout for Wide Attenuation Bands
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Solution Overview
Problem
Existing surface acoustic wave filter devices face challenges in achieving sufficient signal attenuation and a wide attenuation band, as described in Patent Document 1.
Innovation Solution
A filter device is designed with a multilayer substrate, an inductor, and a first open stub. The multilayer substrate includes a first wiring layer, a second wiring layer with a reference electrode, and dielectric layers between them. The inductor is coupled between a first terminal and a second terminal, and the open stub is provided in the first wiring layer, forming a capacitor with the reference electrode and an LC resonant circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a bonding wire stub and first common electrode are used as an open stub connected to package input electrode, then signal attenuation in attenuation band is increased, but sufficient attenuation amount and attenuation band width are difficult to achieve
Solution Approach 1:
The patent transitions from a two-dimensional planar layout to a three-dimensional stacked configuration by placing the open stub and reference electrode on different layers of a multilayer substrate. This vertical stacking enables mutual overlap and capacitor formation, achieving sufficient attenuation and wide attenuation band that cannot be obtained with conventional planar arrangements.
Solution Approach 2:
The patent combines multiple functions into integrated structures: the open stub serves both as an inductor element and forms a capacitor with the reference electrode, creating an LC resonant circuit. This merging of functions reduces component count while achieving the required attenuation performance.
2Reliability
If multiple discrete components are used to achieve sufficient attenuation, then attenuation performance is improved, but device complexity and space requirements increase
Solution Approach 1:
The patent merges the open stub structure with the capacitor formation by positioning it over the reference electrode on a different layer. This integration eliminates the need for separate inductor and capacitor components, reducing device complexity while maintaining sufficient attenuation performance through the formed LC resonant circuit.
Solution Approach 2:
The open stub structure performs multiple functions simultaneously: it acts as an inductor element, forms a capacitor with the reference electrode through mutual overlap, and creates an LC resonant circuit. This multi-functionality reduces the number of discrete components needed while achieving the required attenuation characteristics.
3Ease of manufacture
If conventional planar layout is used for filter components, then manufacturing is simplified, but attenuation band width and signal attenuation are insufficient
Solution Approach 1:
The patent employs a multilayer substrate architecture that stacks wiring layers and dielectric layers vertically, enabling the open stub and reference electrode to overlap in the vertical dimension. This three-dimensional configuration achieves sufficient signal attenuation and wide attenuation band while maintaining manufacturing simplicity through standard multilayer PCB fabrication processes.
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 achieves a sufficient amount of signal attenuation and a wide attenuation band, while also reducing the number of components and space requirements, thus facilitating the design of high-attenuation filters with wide band coverage.
Implementation Method 1
a capacitor is formed by the first reference electrode and the first open stub that mutually overlap
Implementation Method 2
A resonant circuit is formed by the capacitor and the inductor
Data Source
AI summary
A filter device includes a multilayer substrate, an inductor, and a first open stub. The multilayer substrate includes a first wiring layer, a second wiring layer including a first reference electrode to which a reference potential is supplied, and a plurality of first dielectric layers between the first wiring layer and the second wiring layer. The inductor has one end coupled to a first terminal and another end coupled to a second terminal. A portion of the first open stub is provided in the first wiring layer, and the first open stub has one end coupled to the one end of the inductor and another open-circuited end. When the multilayer substrate is viewed in plan view in a stacking direction, a capacitor is formed by the first reference electrode and the first open stub that mutually overlap. A resonant circuit is formed by the capacitor and the inductor.