Multilayer SAW Duplexer Bridging Inductor Area Reduction
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Solution Overview
Problem
Existing SAW duplexers with bridging inductors require large substrates for coil-shaped electrode patterns, limiting size reduction and filter characteristic improvement.
Innovation Solution
A SAW duplexer design with a bridging inductor connected in parallel to a serial arm resonator in the second SAW filter, utilizing a multilayer package substrate with coiled and return wire portions across multiple layers to reduce the inductor's area and increase attenuation, while maintaining or enhancing filter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coil-shaped electrode patterns are formed on the upper surface of the package substrate to create bridging inductors, then the filter characteristics are improved with sufficient attenuation in the opposite passband, but the substrate area increases and size reduction is limited
Solution Approach 1:
The patent transitions from forming inductors on the two-dimensional upper surface to creating three-dimensional multilayer structures within the substrate. Wires are arranged across multiple layers (first layer, second layer, third layer) with via-hole conductors connecting them, effectively utilizing the vertical dimension to reduce the footprint area while maintaining inductor functionality
Solution Approach 2:
The patent embeds the inductor structure within the substrate layers rather than placing it on the surface. The coiled portion formed by wires across multiple layers is nested within the substrate volume, with via-hole conductors penetrating through layers to connect the winding structure, achieving compact integration similar to nested dolls
2Reliability
If bridging inductors are added to improve attenuation in the opposite passband, then filter performance is enhanced, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The inductor structure is segmented into distinct functional components: coiled portions formed by wires on different layers and via-hole conductors connecting them. This segmentation allows each component to be optimized independently while simplifying the overall manufacturing process through standardized layer-by-layer construction
Solution Approach 2:
The multilayer substrate structure serves multiple functions simultaneously: it provides mechanical support, electrical insulation between layers, electrical connection through via-hole conductors, and the inductive function through the coiled wire arrangement. This multi-functionality reduces the need for separate components and simplifies the overall device
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 design achieves size reduction and improved filter characteristics by distributing the bridging inductor's coiled portion across multiple layers, increasing attenuation in the passband and bandwidth without increasing the substrate area, and enhancing isolation between filters.
Implementation Method 1
a bridging inductor is connected in parallel to a serial arm resonator in at least one of the SAW filters
Implementation Method 2
SAW duplexers including first and second SAW filters having different passbands
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
There is provided a SAW duplexer in which a bridging inductor can be formed without increasing the area of a package substrate, which has a good filter characteristic, and which can achieve size reduction. A SAW duplexer (1) includes a first SAW filter having a passband with a relatively low frequency, and a second SAW filter having a passband with a relatively high frequency. The first and second SAW filters each have a ladder-shaped circuit configuration. A bridging inductor is connected in parallel to at least one serial arm resonator in the second SAW filter. The bridging inductor includes a coiled portion provided on a multilayer package substrate. The coiled portion is formed by connecting first to third wires (23, 26, and 29) provided on first to third layers by via-hole conductors. First, third, and fifth via-hole conductors (24, 27, and 30) that form a coil return wire portion are disposed inside the coiled portion.