High Isolation RF Switch With LC Notch Filter
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Solution Overview
Problem
Mobile communication devices face challenges in achieving high isolation between RF switch circuit arms to limit noise leakage and power loss, especially at high frequencies, where conventional shunts are ineffective and add to the device's size and cost.
Innovation Solution
A high isolation RF switch using a switched shunt LC notch filter with a CMOS technology, incorporating a series combination of a capacitor, inductor, and transistors, which provides high isolation while maintaining linearity and allowing for tunable attenuation to configure the switch according to user needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional shunts are used to provide isolation between RF switch arms, then isolation is improved, but device size and cost increase
Solution Approach 1:
The patent transforms the isolation mechanism from physical separation (spatial parameter) to frequency-selective parameter control. By using an LC notch filter tuned to specific frequencies, the system achieves high isolation (40-60 dB) at target frequencies without requiring large physical distances between components, thus resolving the contradiction between isolation performance and device size.
Solution Approach 2:
The LC notch filter acts as an intermediary element between the RF switch arms. Instead of relying on direct physical isolation, the filter mediates the signal paths by selectively attenuating frequencies in the stop band, providing high isolation while occupying minimal space compared to conventional shunt-based approaches.
2Reliability
If conventional shunts are used to provide isolation between RF switch arms, then isolation is improved, but device cost increases
Solution Approach 1:
The patent replaces complex physical isolation structures with a frequency-selective LC notch filter that uses parameter-based filtering. This approach reduces manufacturing complexity and cost while achieving superior isolation performance (40-60 dB) compared to conventional shunt methods, directly addressing the cost-isolation tradeoff.
Solution Approach 2:
The patent substitutes mechanical/physical isolation mechanisms (conventional shunts requiring physical separation) with an electrical/filter-based mechanism (LC notch filter). This substitution reduces both manufacturing complexity and device cost while maintaining or improving isolation performance.
3Reliability
If physical separation of components is increased to reduce noise leakage, then isolation is improved, but device size increases
Solution Approach 1:
The patent shifts from spatial parameter (physical separation distance) to frequency parameter (notch filter tuning) for noise reduction. The LC notch filter provides 40-60 dB attenuation of noise and interference at specific frequencies without requiring increased physical separation between components, thus reducing device volume while improving noise reduction performance.
4Volume of moving object
If RF switch is located in close proximity to antenna to reduce device size, then device compactness is improved, but noise leakage and harmonic interference increase
Solution Approach 1:
The LC notch filter serves as an intermediary between the RF switch and antenna, enabling close proximity placement while mitigating noise leakage and harmonic interference. The filter's frequency-selective attenuation provides 40-60 dB isolation of harmful signals, allowing compact integration without sacrificing performance.
Solution Approach 2:
The patent converts the potential harm of close proximity (noise leakage) into a benefit by using the LC notch filter to selectively attenuate harmful frequencies. The filter transforms the noise problem into a controlled frequency-selective filtering solution, enabling compact design while eliminating interference.
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 solution achieves very high isolation (over 40 dB) between circuit arms, reducing noise and power loss while maintaining a compact size, and is adaptable to different frequency bands and communication standards.
Implementation Method 1
The at least one LC notch filter comprises a series combination of a switch, at least one capacitor and at least one inductor, and is configured to attenuate signals within a stop band range of frequencies determined by a value of the at least one capacitor and a value of the at least one inductor
Data Source
AI summary
A switching method and apparatus that provides high isolation between circuit arms of a mobile communication device by attenuating noise over a defined frequency range using a switched shunt LC notch filter.