Acoustic Wave Reflector Pitch Layout for Low-Frequency Ripple Control
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Solution Overview
Problem
Existing acoustic wave filters in multi-band systems face challenges in minimizing return loss and ripple on the lower frequency side, which affects the miniaturization and isolation requirements in mobile phone front-end circuits.
Innovation Solution
The design incorporates a piezoelectric substrate with an IDT electrode and a reflector, where the electrode-finger pitch of the reflector is greater than that of the IDT electrode, and the center-to-center distance between adjacent electrode fingers is optimized to reduce or prevent ripples by varying the electrode-finger pitches, specifically making the first to k-th pitches less than the subsequent pitches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the center-to-center distance between the IDT electrode and reflector is reduced to suppress return loss increase, then return loss on the lower frequency side is improved, but ripple appears in the partial band
Solution Approach 1:
The reflector electrode fingers are designed with non-uniform spacing, where the distance between adjacent reflector electrode fingers varies along the acoustic wave propagation direction. Specifically, the distance between the IDT electrode and the first reflector electrode finger is smaller than the distance between subsequent reflector electrode fingers. This local variation in spacing allows different regions of the reflector to serve different functions: the region closer to the IDT suppresses return loss, while the region farther away controls ripple, thereby resolving the contradiction between suppressing return loss and preventing ripple.
2Productivity
If multiple filter devices are arranged in the front-end circuit to support multi-band transmission, then data transmission rate is improved, but mounting space is consumed
Solution Approach 1:
The acoustic wave filter device is designed with a reflector that serves multiple functions simultaneously: it reflects acoustic waves to form resonant cavities, suppresses return loss through optimized spacing, and controls ripple through non-uniform finger spacing. This multi-functionality allows a single filter device to achieve performance that would otherwise require multiple separate components, thereby reducing the number of filter devices needed in the front-end circuit and reducing mounting space while maintaining multi-band transmission capability.
3Object-generated harmful factors
If the electrode-finger pitch of the reflector is increased to reduce ripple, then ripple suppression is improved, but the center-to-center distance requirement becomes more restrictive
Solution Approach 1:
The reflector electrode fingers are segmented into regions with different spacing characteristics. The segmentation creates a gradient structure where spacing increases progressively from the IDT electrode outward. This segmentation allows the system to achieve ripple suppression through larger overall pitch while maintaining compliance with the center-to-center distance requirement by having smaller initial spacing near the IDT, thus resolving the contradiction between ripple reduction and distance constraints.
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 reduces or prevents ripples on the frequency side lower than the resonant frequency, enhancing the insertion loss characteristics and meeting the requirements for miniaturization and high isolation in mobile phone front-end circuits.
Implementation Method 1
an acoustic wave element according to a preferred embodiment of the present invention includes a piezoelectric substrate, an IDT electrode provided on the piezoelectric substrate
Implementation Method 2
a reflector located adjacent to the IDT electrode in an acoustic wave propagation direction
Data Source
AI summary
An acoustic wave element includes an electrode-finger pitch of reflecting-electrode fingers greater than an electrode-finger pitch pi of comb-shaped electrode fingers, and a center-to-center distance between a reflecting-electrode finger and a comb-shaped electrode finger is equal to or less than about 0.9 times the electrode-finger pitch of the reflecting-electrode fingers. When a reflecting-electrode finger counted from a closest reflecting-electrode finger is designated as a k-th reflecting-electrode finger in order, a reflecting-electrode finger farthest from the IDT electrode is defined as an (n+1)-th reflecting-electrode finger, and an electrode-finger pitch between the k-th reflecting-electrode finger and a (k+1)-th reflecting-electrode finger is defined as a k-th electrode-finger pitch pk, a value of electrode-finger pitches from a first electrode-finger pitch p1 to the k-th electrode-finger pitch pk is less than a value of electrode-finger pitches from a (k+1)-th electrode-finger pitch pk+1 to an n-th electrode-finger pitch pn.