Transmit Filter Circuit Intermodulation Distortion Suppression
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Solution Overview
Problem
Existing mobile communication device filter circuits, such as ladder filter circuits, fail to effectively manage third-order intermodulation distortion, which can degrade reception sensitivity by allowing noise to enter the receive signal band.
Innovation Solution
A transmit filter circuit design that includes multiple series arm resonators and a parallel arm resonator, where the resonant frequency of the first series arm resonator closest to the output terminal is higher than the second series arm resonator, effectively attenuating interference waves and reducing third-order intermodulation distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ladder filter circuit with multiple resonators is used to separate transmit and receive signals, then signal separation is achieved, but third-order intermodulation distortion occurs when interference waves mix with the transmit signal
Solution Approach 1:
The patent applies local quality by making each resonator have different characteristics (different resonant frequencies and different Q values) to perform specialized functions. The first resonator is designed with specific parameters to suppress interference waves in a particular frequency range, while the second resonator handles different frequency components, creating localized optimization throughout the filter circuit to reduce intermodulation distortion overall
Solution Approach 2:
The patent uses composite materials by combining multiple resonator elements with different properties into a unified filter circuit. The first resonator and second resonator are composite components with different resonant frequencies and Q values that work together to achieve both signal separation and intermodulation distortion suppression, effectively creating a composite filtering system
2Manufacturing precision
If the resonator is designed to attenuate signals in other frequency bands, then frequency selectivity is improved, but interference waves with frequency close to transmit signal are not sufficiently suppressed
Solution Approach 1:
The patent segments the filtering function into multiple resonators with different characteristics. Instead of relying on a single resonator to handle all frequency selection and interference suppression, the circuit divides this task between the first resonator (optimized for interference suppression) and the second resonator (optimized for frequency selectivity), allowing each component to specialize in its particular function
Solution Approach 2:
The patent applies parameter changes by setting different resonant frequencies and different Q values for the first and second resonators. The first resonator has parameters optimized for suppressing interference waves close to the transmit frequency, while the second resonator has parameters optimized for the desired frequency band, allowing precise control over both interference suppression and frequency selectivity
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
The design significantly reduces third-order intermodulation distortion by inhibiting interference waves from entering the filter circuit, thereby improving reception sensitivity without significantly increasing insertion loss or circuit area.
Implementation Method 1
a ladder filter circuit including multiple resonators having different resonant frequencies and different anti-resonant frequencies
Data Source
AI summary
A transmit filter circuit includes an input terminal, an output terminal, plural series arm resonators, and a parallel arm resonator. The input terminal receives a transmit signal. The output terminal is electrically connected to an antenna. The plural series arm resonators are electrically connected in series with each other on a line between the input and output terminals. The plural series arm resonators include first and second series arm resonators. The first series arm resonator is closest to the output terminal. The second series arm resonator is second closest to the output terminal. A first end of the parallel arm resonator is electrically connected to a node between the first and second series arm resonators. A reference potential is provided to a second end of the parallel arm resonator. The resonant frequency of the first series arm resonator is higher than that of the second series arm resonator.