Acoustic Wave Filter TCF Tuning at Passband Edges
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Solution Overview
Problem
RF filters in communication devices face challenges in maintaining sharp frequency band boundaries that do not shift significantly with temperature changes, especially in scenarios with narrowly spaced frequency bands like LTE and WiFi, leading to potential interference.
Innovation Solution
The design incorporates a series of acoustic wave resonators with varying dielectric film thicknesses on interdigital transducer electrodes, allowing for specific tuning of temperature coefficients of frequency (TCF) at passband edges, ensuring stability and maintaining passband width across temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If acoustic wave resonators with uniform dielectric film thickness are used, then the filter structure is simple and easy to manufacture, but the temperature coefficient of frequency (TCF) stability at passband edges deteriorates
Solution Approach 1:
The patent applies local quality by varying the dielectric film thickness selectively at different locations of the interdigital transducer electrodes. Specifically, the dielectric film thickness is adjusted in regions corresponding to different resonators to achieve different TCF values for each resonator, thereby improving TCF stability at passband edges while maintaining overall structural simplicity
Solution Approach 2:
The patent changes the physical parameter of dielectric film thickness to control and tune the TCF of individual resonators. By modifying this parameter locally, the patent achieves different TCF characteristics for different resonators, enabling improved temperature stability at passband edges without fundamentally changing the filter structure
2Productivity
If the bandgap between frequency bands is narrowed to utilize all available bandwidth, then spectral efficiency is improved, but frequency band boundaries become less distinct and interference increases
Solution Approach 1:
The patent replaces conventional resonators with acoustic wave resonators that have engineered TCF characteristics. This substitution enables precise control over frequency response and sharp boundary definition, allowing narrow bandgaps to be utilized effectively while maintaining distinct frequency band boundaries and reducing interference through the resonators' inherent filtering properties
3Device complexity
If conventional resonators are used without TCF compensation, then device complexity is reduced, but frequency shifts due to temperature changes increase
Solution Approach 1:
The patent implements local quality by applying varying dielectric film thicknesses to different portions of the interdigital transducer electrodes. This local variation creates resonators with different TCF values, allowing frequency compensation and stability improvement without adding complex external compensation circuits or mechanisms
Solution Approach 2:
The patent enables self-service by designing resonators that automatically compensate for temperature-induced frequency shifts through their inherent TCF characteristics. The varying dielectric film thicknesses create resonators with complementary TCF properties that self-correct frequency drift, eliminating the need for external temperature compensation mechanisms
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 approach results in RF filters with improved TCF stability at both upper and lower passband edges, reducing frequency shifts due to temperature changes while maintaining wide passbands, thus enhancing the operation of devices with narrow bandgaps between transmission and reception frequency bands.
Implementation Method 1
surface acoustic wave (SAW) resonators having interdigital transducer (IDT) electrodes disposed on a piezoelectric substrate
Implementation Method 2
surface acoustic wave (SAW) resonators having interdigital transducer (IDT) electrodes disposed on a piezoelectric substrate
Data Source
AI summary
An electronic filter includes a plurality of series arm acoustic wave resonators electrically connected in series between an input port and an output port, a plurality of parallel arm acoustic wave resonators electrically connected in parallel and electrically connected on first sides between respective ones of the plurality of series arm acoustic wave resonators and electrically connected on second sides to ground, and at least one additional acoustic wave resonator electrically connected in parallel to one of one of the plurality of series arm acoustic wave resonators or one of the plurality of parallel arm acoustic wave resonators and having a temperature coefficient of frequency (TCF) lower than a TCF of the acoustic wave resonator to which it is electrically connected in parallel.