Acoustic Wave Filter IDT Pitch Layout to Prevent LC Resonance
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Solution Overview
Problem
In communication devices, acoustic wave filters connected in common can experience a decrease in attenuation due to LC resonance, leading to impedance matching issues and reduced performance in pass bands of other filters.
Innovation Solution
The design includes a series resonator or longitudinally coupled resonator connected to a plurality of parallel resonators, where the IDT electrode of one parallel resonator has varying electrode finger pitches, ensuring it remains inductive between resonant and anti-resonant frequencies, preventing LC resonance and maintaining attenuation across connected filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If parallel resonators with different resonant frequencies are used to achieve sharp transition band, then the sharpness of transition band is improved, but LC resonance occurs in frequency bands between resonant frequencies causing impedance to approach 50Ω and attenuation to decrease
Solution Approach 1:
The patent applies local quality by making each parallel resonator have non-uniform electrode finger pitches within its IDT electrode. Specifically, the electrode fingers have different pitches in different regions, creating local variations in resonant characteristics. This allows each resonator to have a broader impedance variation range while maintaining the overall sharp transition band when multiple resonators are combined, preventing LC resonance issues in connected filters.
Solution Approach 2:
The patent changes the parameter of electrode finger pitches from uniform to non-uniform distribution. By varying the pitches of electrode fingers within each parallel resonator's IDT electrode, the resonant frequencies and impedance characteristics are modified. This parameter change enables each resonator to contribute to a broader frequency response while maintaining sharp overall transitions, resolving the contradiction between sharpness and attenuation reliability.
2Adaptability or versatility
If acoustic wave filters are connected in common in a multiplexer to enable multiband operation, then device versatility is improved, but attenuation decreases in pass bands of other filters due to LC resonance
Solution Approach 1:
By implementing non-uniform electrode finger pitches within each parallel resonator, the patent creates local variations in resonant characteristics. This allows each resonator to have a broader impedance variation range, which when combined in a multiplexer, prevents LC resonance from occurring in the pass bands of other connected filters, thereby maintaining reliable attenuation across all frequency bands.
Solution Approach 2:
The patent modifies the electrode finger pitch parameters to be non-uniform within each resonator. This parameter change broadens the impedance variation range of each resonator, enabling the filter to maintain proper attenuation characteristics when multiple filters are connected in common for multiband operation, thus resolving the versatility-reliability contradiction.
3Length of moving object
If parallel resonators are divided in parallel with different resonant frequencies to achieve narrow pass band, then pass band width is reduced, but impedance approaches 50Ω in frequency bands between resonant frequencies causing attenuation decrease
Solution Approach 1:
The patent applies local quality by introducing non-uniform electrode finger pitches within each parallel resonator's IDT electrode. This creates local variations in resonant characteristics that broaden the impedance variation range of each resonator. When multiple such resonators are connected in parallel, they maintain narrow overall pass band width while avoiding impedance matching to 50Ω in between-resonant frequency bands, thus preventing attenuation decrease.
Solution Approach 2:
By changing the electrode finger pitch parameter from uniform to non-uniform distribution within each resonator, the patent broadens the individual resonator's impedance variation range. This parameter change allows the parallel combination to achieve both narrow pass band width and reliable attenuation by preventing LC resonance conditions in the attenuation bands.
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 enhances the sharpness of the transition band from pass to stop bands, reduces return loss, and prevents attenuation decreases in connected filters, improving receiver sensitivity and filter performance.
Implementation Method 1
Each of the first parallel resonator and the second parallel resonator includes an IDT electrode including a plurality of electrode fingers extending in a direction intersecting with a propagation direction of an acoustic wave
Implementation Method 2
An acoustic wave resonator is inductive in a frequency band between a resonant frequency and an anti-resonant frequency thereof, and is capacitive in a frequency band lower than the resonant frequency and in a frequency band higher than the anti-resonant frequency
Data Source
AI summary
A filter includes a series resonator or a longitudinally coupled resonator on a path connecting a first input-and-output terminal and a second input-and-output terminal, and parallel resonators each connected between the path and a ground. Among the parallel resonators, a second parallel resonator and a first parallel resonator are connected in parallel without another resonator being interposed therebetween. An IDT electrode of the first parallel resonator includes different electrode finger pitches. An average of all the electrode finger pitches of the IDT electrode of the first parallel resonator is larger than an average of all the electrode finger pitches of an IDT electrode of the second parallel resonator.