SAW Ladder Filter Gap Hammer Layout for Spurious Mode Suppression
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Solution Overview
Problem
Existing radio frequency filters, such as surface acoustic wave (SAW) filters, face challenges in suppressing transverse mode spurious signals while maintaining optimal insertion loss, particularly when using higher density materials like tungsten for IDT electrodes, which exacerbate spurious signal strength.
Innovation Solution
Incorporating gap hammer structures in selected series and shunt SAW resonators, with specific resonance frequencies, to suppress transverse mode spurious signals while minimizing degradation in insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If gap hammer structures are added to all series arm SAW resonators to suppress transverse mode spurious signals, then spurious signal suppression is improved, but insertion loss deteriorates
Solution Approach 1:
The patent applies gap hammer structures selectively to specific series arm resonators based on their resonance frequencies. Resonators with lower resonance frequencies (which generate stronger spurious signals) receive gap hammer structures, while higher frequency resonators maintain simpler designs. This localized application optimizes spurious signal suppression where most needed while preserving insertion loss performance in other parts of the filter.
2Reliability
If higher density materials like tungsten are used for IDT electrodes to improve electrode performance, then electrode conductivity is improved, but transverse mode spurious signals are exacerbated
Solution Approach 1:
The patent acknowledges that higher density materials like tungsten inherently generate stronger spurious signals, but converts this challenge into a design criterion. By identifying which resonators are most susceptible to spurious signals (those with lower resonance frequencies), the patent applies gap hammer structures specifically to these resonators, transforming the material's harmful effect into a targeted design parameter that drives selective suppression strategies.
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 solution effectively reduces spurious signals while maintaining or improving insertion loss characteristics in ladder filters, enabling smaller and more efficient SAW resonators for use in electronic devices.
Implementation Method 1
a first plurality of series arm surface acoustic wave resonators electrically connected in series between an input of the filter and an output of the filter
Implementation Method 2
one or more of the plurality of series arm surface acoustic wave resonators including gap hammer structures to suppress transverse mode spurious signals
Data Source
AI summary
Aspects and embodiments disclosed herein include a radio frequency ladder filter comprising a plurality of series arm surface acoustic wave resonators electrically connected in series between an input of the filter and an output of the filter, and a plurality of shunt surface acoustic wave resonators each electrically connected between nodes between adjacent one of the plurality of series arm surface acoustic wave resonators and ground, one or more of the plurality of series arm surface acoustic wave resonators including gap hammer structures, a remaining one or more of the plurality of series arm surface acoustic wave resonators lacking gap hammer structures to improve insertion loss characteristics of the filter.