SAW Filter Output Impedance Tuning for Low-Noise RF Modules
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Solution Overview
Problem
High-frequency modules face challenges in reducing both loss and noise due to limitations in adjusting the output impedance of surface acoustic wave filters, as altering the intersecting width or number of IDT electrode pairs either increases signal loss or degrades voltage standing wave ratio.
Innovation Solution
A high-frequency module with a longitudinally coupled surface acoustic wave filter and a low-noise amplifier, where the output impedance is adjusted between specific values to minimize loss and noise, using electrode parameters such as the number of withdrawal electrodes, main wavelength ratio, and duty cycle to achieve impedance matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the intersecting width of IDT electrodes is increased to adjust output impedance, then the noise of the surface acoustic wave filter is reduced, but the resistance of electrode fingers increases, thus increasing signal loss
Solution Approach 1:
The patent changes the geometric parameters of the IDT electrodes, specifically the intersecting width, to adjust the output impedance of the surface acoustic wave filter. By optimizing this parameter, the filter achieves better impedance matching with the low-noise amplifier, reducing noise while controlling signal loss through careful parameter selection.
2Object-affected harmful factors
If the number of pairs of electrode fingers in IDT electrodes is increased to adjust output impedance, then the noise of the surface acoustic wave filter is reduced, but the resonant mode spacing becomes narrow, thus narrowing the pass band width
Solution Approach 1:
The patent adjusts the number of pairs of electrode fingers in the IDT electrodes to modify the output impedance characteristics. This parameter change enables the filter to achieve optimal impedance matching, reducing noise while maintaining an acceptable pass band width through careful optimization of the electrode finger count.
3Productivity
If the number of pairs of electrode fingers in IDT electrodes is decreased to adjust output impedance, then the resonant mode spacing becomes wide, but the voltage standing wave ratio characteristics are degraded, thus increasing signal loss
Solution Approach 1:
The patent optimizes the number of pairs of electrode fingers to achieve a balance between resonant mode spacing and voltage standing wave ratio characteristics. By carefully selecting this parameter, the filter achieves improved impedance matching and resonant properties while minimizing signal loss through optimal parameter configuration.
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 effectively reduces both loss and noise in the high-frequency module by optimizing the output impedance of the surface acoustic wave filter, enhancing the overall transmission characteristics and impedance matching with the low-noise amplifier.
Implementation Method 1
a high-frequency module including a surface acoustic wave (SAW) filter has been developed as a circuit module for a mobile communication device
Implementation Method 2
a low-noise amplifier that is connected to the surface acoustic wave filter and that amplifies a high-frequency signal that has passed through the surface acoustic wave filter
Data Source
AI summary
A high-frequency module includes a longitudinally coupled surface acoustic wave filter and a low-noise amplifier that is connected to the surface acoustic wave filter. The input impedance of the surface acoustic wave filter connected to the low-noise amplifier differs from the output impedance thereof. On a Smith chart, the output impedance in the pass band of the surface acoustic wave filter is present in a region between a first output impedance and a second output impedance, the first output impedance being the output impedance of the surface acoustic wave filter where a gain of the low-noise amplifier is maximum, the second output impedance being the output impedance of the surface acoustic wave filter where a noise figure of the low-noise amplifier is minimum.