Series-Connected SAW Filter Electrode Layout for Out-of-Band Attenuation
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Solution Overview
Problem
Surface acoustic wave filters with series-connected interdigital transducers (IDTs) suffer from inadequate out-of-passband attenuation due to capacitive coupling between adjacent IDTs, leading to filter damage and reduced power handling capability.
Innovation Solution
The design includes a surface acoustic wave filter with a configuration where at least one electrode finger of the input/output electrode is adjacent to the ground electrode, allowing electric current to flow to the ground and minimizing leakage between adjacent IDTs, thereby enhancing bandpass characteristics and power handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a floating electrode is interposed between input/output electrode and ground electrode in series-connected IDTs, then power handling capability is enhanced, but capacitive coupling between adjacent electrode fingers causes leakage current and inadequate out-of-passband attenuation
Solution Approach 1:
The harmful capacitive coupling effect is extracted and eliminated by removing the floating electrode structure that caused it. The patent replaces the floating electrode with a direct series connection between IDTs, taking out the source of leakage current while preserving the power handling enhancement through the series-connected configuration.
Solution Approach 2:
The patent converts the harmful capacitive coupling effect into a beneficial series-connected configuration. By eliminating the floating electrode, the adjacent electrode fingers are reconfigured to create intentional series capacitance that enhances power handling while preventing leakage current, thus converting a harmful effect into a useful one.
2Power
If floating electrode structure is used in IDTs, then power handling capability improves, but out-of-passband attenuation deteriorates due to leakage current
Solution Approach 1:
The floating electrode structure is extracted and removed from the design. The patent implements a direct series connection between adjacent IDTs without floating electrodes, thereby eliminating the leakage current path while maintaining the power handling capability through the series configuration.
Solution Approach 2:
The harmful leakage current effect is converted into beneficial series-connected operation. The adjacent electrode fingers are configured to create series capacitance that enhances power handling and simultaneously provides proper isolation for out-of-passband attenuation, transforming the harmful capacitive coupling into a useful filtering mechanism.
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 suppresses leakage current between adjacent IDTs, improving out-of-passband attenuation and achieving better bandpass characteristics and electric characteristics in surface acoustic wave filters and duplexers.
Implementation Method 1
A surface acoustic wave (SAW for short) is a wave which propagates with energy concentration around the surface of an elastic body, and a filter element utilizing this wave is called 'surface acoustic wave filter'
Implementation Method 2
a plurality of series-connected type IDT electrodes formed on one main surface of a piezoelectric substrate
Data Source
AI summary
A surface acoustic wave filter and a duplexer are provided. In a surface acoustic wave filter, on a piezoelectric substrate, a first IDT electrode composed of an input/output electrode and a first floating electrode, and a second IDT electrode composed of a ground electrode and a second floating electrode are arranged, and are connected in series to each other via the first floating electrode and the second floating electrode to form IDTs. In two serial IDTs arranged next to each other, an electrode finger of the input/output electrode in the first IDT electrode of one serial IDT is arranged next to an electrode finger of the ground electrode in the second IDT electrode of the other serial IDT.