Multi-Mode SAW Filter Impedance Conversion for Compact RF Filtering
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Solution Overview
Problem
The challenge of reducing the size of acoustic wave filters in radio frequency systems while maintaining high performance and avoiding degradation in filter rejection and ruggedness, particularly in the context of increasing frequency bands in 4G and 5G technologies, is addressed.
Innovation Solution
The implementation of a multi-mode surface acoustic wave filter with a ladder section, featuring a higher impedance at the output than the input, and a design with more input tracks and IDT electrode fingers than output tracks, along with a matching network and ladder section, allows for impedance transformation and reduced filter size without compromising performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the size of acoustic wave filters is reduced, then the filter area is decreased, but the filter rejection and ruggedness are degraded
Solution Approach 1:
The patent changes the impedance parameter of the filter by designing the multi-mode SAW filter to have a higher output impedance than input impedance. This parameter change enables the use of a ladder section with fewer elements, thereby reducing the overall filter area while maintaining the necessary filter rejection and ruggedness performance.
Solution Approach 2:
The patent employs a composite structure combining a multi-mode SAW filter with a ladder section. This composite design leverages the high impedance transformation capability of the multi-mode SAW filter and the filtering characteristics of the ladder section to achieve compact size without compromising performance.
2Power
If the number of input tracks and IDT electrode fingers is increased, then the input impedance is decreased, but the output impedance becomes higher
Solution Approach 1:
The patent introduces asymmetry in the filter design by having a different number of tracks and IDT electrode fingers at the input compared to the output. Specifically, the input has more tracks and fingers than the output, creating an asymmetric structure that achieves the desired impedance transformation from lower input impedance to higher output impedance.
3Reliability
If a ladder section is added to the multi-mode SAW filter, then the filter performance is improved, but the device complexity increases
Solution Approach 1:
The patent extracts only the essential filtering elements needed to achieve the desired performance by using a simplified ladder section with fewer series and shunt resonators. This selective extraction approach improves filter performance while minimizing the increase in device complexity.
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 design achieves a smaller filter size with improved power handling, reduced noise floor, and better gamma (S11) performance, while maintaining or enhancing filter performance specifications.
Implementation Method 1
A SAW resonator is arranged to generate a surface acoustic wave
Implementation Method 2
An acoustic wave filter can include a plurality of acoustic wave resonators arranged to filter a radio frequency signal. Example acoustic wave filters include surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters. A SAW resonator of a SAW filter typically includes an interdigital transductor electrode on a piezoelectric substrate.
Data Source
AI summary
Aspects of this disclosure relate to an acoustic wave filter that includes a multi-mode surface acoustic wave filter and a ladder section. The multi-mode surface acoustic wave filter has a higher impedance at an output than at an input. The ladder section is connected to the output of the multi-mode surface acoustic wave filter. Related radio frequency systems, radio frequency modules, wireless communication devices, and methods are disclosed.