Acoustic Wave Filter Gap Tuning for Out-of-Band Attenuation
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Solution Overview
Problem
Acoustic wave filters with additional circuits experience strong excitation, leading to deterioration of attenuation characteristics outside the pass band.
Innovation Solution
The acoustic wave filter design includes an additional circuit with a specific relationship between the array pitches of comb-shaped electrode fingers and reflector electrode fingers, ensuring a phase shift between IDTs and reflectors to prevent overexcitation, thereby maintaining effective attenuation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an additional circuit is connected in parallel with the filter circuit to generate cancel signals for out-of-band frequencies, then attenuation characteristics outside the pass band are improved, but strong excitation occurs in the additional circuit causing deterioration of attenuation characteristics
Solution Approach 1:
The patent applies parameter changes by optimizing the gap distance between IDT electrode fingers and reflector electrode fingers. Specifically, the gap G is set to satisfy 0.35λ ≤ G ≤ 0.50λ, where λ is the acoustic wave wavelength. This parameter optimization prevents strong excitation in the additional circuit while maintaining effective attenuation characteristics outside the pass band.
Solution Approach 2:
The patent uses reflectors that replicate the electrode finger structure of the IDT but with opposite polarity. The reflector electrode fingers are arranged to mirror the IDT electrode fingers, creating a symmetric structure that generates cancel signals for out-of-band frequencies without causing strong excitation when the gap is properly controlled.
2Object-generated harmful factors
If the gap between IDT and reflector is reduced to prevent overexcitation, then strong excitation is suppressed, but the ability to generate effective cancel signals may be compromised
Solution Approach 1:
The patent identifies and optimizes the critical parameter of the gap distance between IDT and reflector. By setting the gap G within the specific range of 0.35λ ≤ G ≤ 0.50λ, the patent simultaneously achieves suppression of strong excitation and maintenance of effective cancel signal generation for out-of-band frequencies.
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 reduces or prevents deterioration of attenuation characteristics outside the pass band by preventing overexcitation in the acoustically-coupled resonator, enhancing the filter's performance.
Implementation Method 1
Each of the comb-shaped electrodes includes a plurality of comb-shaped electrode fingers extending in a first direction parallel or substantially parallel to a main surface of the piezoelectric substrate
Implementation Method 2
The plurality of reflectors are located on both outer sides of the plurality of IDTs in the second direction and each include a plurality of reflector electrode fingers extending in the first direction
Implementation Method 3
A relationship of about 0.60+n≤G/(Pi+Pr)≤0.93+n is satisfied, where n is an integer of 0 or more, Pi denotes an array pitch of the plurality of comb-shaped electrode fingers along the second direction, Pr denotes an array pitch of the plurality of reflector electrode fingers along the second direction, and G denotes, in a boundary region between the IDT and the reflector, an IDT-reflector gap
Data Source
AI summary
An acoustic wave filter includes a filter circuit and an additional circuit that includes IDTs and reflectors. The IDTs each include comb-shaped electrode fingers. The reflectors each include reflector electrode fingers. A relationship of about 0.60+n≤G/(Pi+Pr)≤0.93+n is satisfied, where n is an integer of 0 or more, Pi is an array pitch of the comb-shaped electrode fingers arranged along a second direction, Pr is an array pitch of the reflector electrode fingers arranged along the second direction, and G denotes, in boundary regions between the IDTs and the reflectors, an IDT-reflector gap, which is a center-to-center distance between a comb-shaped electrode finger closest to the reflectors and a reflector electrode finger closest to the IDTs.