Elastic Wave Filter Impedance Tuning for Low-Noise RF Modules
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Solution Overview
Problem
RF modules with LNAs face challenges in maintaining optimal noise figure and gain characteristics across the passband, as the impedance for maximum gain differs from the impedance for minimum noise figure, leading to deteriorated transmission characteristics at the frequency ends.
Innovation Solution
The RF module incorporates an elastic wave filter with an output impedance positioned closer to the noise matching impedance at the low and high frequency ends of the passband, using a longitudinally-coupled filter structure and adjustable electrode parameters to align with both gain and noise matching impedances, thereby optimizing the noise figure and gain characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the filter circuit and LNA are subjected to impedance matching by the matching circuit such that the gain becomes maximum with respect to the passband of the filter circuit, then the gain of the LNA becomes maximum, but the noise figure of the LNA deteriorates particularly at an end of the passband
Solution Approach 1:
The patent applies local quality by setting different impedance matching conditions at different frequency regions. Specifically, the output impedance of the elastic wave filter is designed to be closer to the noise matching impedance at the low frequency end and/or high frequency end of the passband, while maintaining appropriate impedance characteristics in the center frequency region. This frequency-dependent impedance optimization locally improves noise figure at the band edges without significantly compromising overall gain performance.
2Object-affected harmful factors
If the output impedance of the elastic wave filter is positioned closer to the noise matching impedance at the frequency ends of the passband, then the noise figure of the LNA decreases at these frequencies, but this requires precise impedance control that complicates the filter design
Solution Approach 1:
The patent employs parameter changes by adjusting the output impedance of the elastic wave filter based on the positional relationship between noise matching impedance and gain matching impedance on the Smith chart. The output impedance is optimized to be closer to the noise matching impedance at frequency ends where noise figure deterioration occurs, while maintaining overall system performance. This parameter optimization achieves noise figure improvement without requiring complex additional circuit structures.
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 decreases the noise figure at the frequency ends, improving the overall transmission characteristics of the RF module by aligning the output impedance with noise matching impedance, thus achieving better performance across the passband.
Implementation Method 1
an elastic wave filter, and a low-noise amplifier (LNA) that amplifies an RF signal output from the elastic wave filter
Data Source
AI summary
A radio frequency module includes an elastic wave filter and a low-noise amplifier that amplifies an RF signal output from the elastic wave filter. An output impedance of the elastic wave filter is positioned, on a Smith chart, closer to a noise matching impedance than to a gain matching impedance, at a frequency of at least one of a low frequency end and a high frequency end of a passband of the elastic wave filter. The noise matching impedance indicates the output impedance where a noise figure of the LNA becomes minimum. The gain matching impedance indicates the output impedance where a gain of the LNA becomes maximum.