Balanced IDT Chirping in Acoustic Resonators for Spur Control
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Solution Overview
Problem
Current radio frequency (RF) filters face challenges in operating effectively at higher frequency bands while maintaining low signal loss and rejecting unwanted frequencies, particularly due to the impact of spurs on their resonance response.
Innovation Solution
The implementation of chirping techniques in acoustic resonators, where the pitch and width of IDT fingers are varied along the length of the interdigital transducer, spreads out the impact of spurs on the resonance response, allowing the filter to operate across different frequency bands without increasing loss near resonance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If chirping is applied to spread out spur impact, then filter can operate at different frequency bands, but frequency shift of main mode increases causing increased loss near resonance
Solution Approach 1:
The patent applies parameter changes by implementing two types of chirping with different rates: mark chirp (changing finger width) and pitch chirp (changing finger spacing). By carefully selecting the ratio between mark chirp rate and pitch chirp rate, the patent achieves cancellation of main mode frequency shift while still spreading out spur impact, thus operating at different frequency bands without increasing loss near resonance
Solution Approach 2:
The patent uses the anti-weight principle by having mark chirp and pitch chirp act in opposite directions on the main mode frequency. The frequency shift caused by mark chirp is counterbalanced by the frequency shift caused by pitch chirp, resulting in net cancellation of main mode frequency shift. This allows spur spreading while maintaining stable main mode operation
2Reliability
If mark chirp is increased to reduce spur sensitivity, then filter performance improves, but main mode frequency stability deteriorates
Solution Approach 1:
The patent applies the anti-weight principle by introducing pitch chirp to counterbalance the frequency shift effect of mark chirp on the main mode. While mark chirp reduces spur sensitivity by spreading out spur impact, its frequency shift effect on the main mode is counteracted by pitch chirp, thereby maintaining main mode frequency stability
Solution Approach 2:
The patent uses parameter changes by optimizing the ratio between mark chirp rate and pitch chirp rate. This controlled parameter adjustment allows the system to achieve reduced spur sensitivity through mark chirp while compensating for main mode frequency drift through pitch chirp, thus improving reliability without sacrificing frequency stability
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 cancels the frequency shift of the main mode, reducing spur sensitivity and maintaining low loss near resonance, thereby enhancing the filter's performance across various frequency bands.
Implementation Method 1
a piezoelectric layer supported by the substrate
Implementation Method 2
an interdigital transducer (IDT) at a surface of the piezoelectric layer. In this aspect, the IDT includes a first busbar and a second busbar that each extend in a first direction from a first end to a second end thereof, a first plurality of electrode fingers extending from the first busbar in a second direction towards the second busbar
Implementation Method 3
chirping is a technique for acoustic resonators used to spread out the impact of spurs on a filter response and improve the overall filter to operate at different frequency bands
Data Source
AI summary
An acoustic resonator is provided that includes a substrate; a piezoelectric layer supported by the substrate; and an interdigital transducer (IDT) at a surface of the piezoelectric layer. The IDT includes a pair of busbars and a plurality of electrode fingers extending from the first and second busbars to be interleaved with each other. The respective widths of at least a portion of the electrode fingers increases in a direction from respective first ends of the first and second busbars to the respective second end of the first and second busbars. Moreover, a pitch of the portion of the electrode fingers decreases in the direction from the respective first ends of the first and second busbar to the respective second ends of the first and second busbars.