RF Switch Impedance Control for Parasitic Leakage Reduction
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Solution Overview
Problem
RF switches in existing transceivers face issues with parasitic leakage due to high-power transmitted signals and inability to handle high voltages, particularly when both power and receiver amplifiers are coupled to the same switch, leading to unintended coupling and harmonic interference.
Innovation Solution
The implementation of a CMOS-based RF switching device with double-gate semiconductor valves that control impedance on transmission lines, allowing for alternate coupling of antennas to either a transmitter or receiver amplifier, thereby minimizing parasitic leakage and harmonic interference by using valves that can be controlled to switch on and off, reducing insertion loss and providing significant isolation at primary frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single switch is used to couple both power amplifier and receiver amplifier to the antenna, then device complexity is reduced, but parasitic leakage increases and receiver sensitivity deteriorates
Solution Approach 1:
The patent divides the single switch into two separate switches: a first switch coupling the power amplifier to the antenna, and a second switch coupling the receiver amplifier to the antenna. This segmentation isolates the high-power transmitted signal path from the sensitive receiver path, preventing parasitic leakage from the power amplifier from interfering with the receiver while maintaining overall system functionality.
2Ease of manufacture
If MOS switches are used for RF switching, then ease of manufacture is improved, but voltage handling capability worsens due to inability to withstand high voltages
Solution Approach 1:
The patent changes the electrical parameters of the switch by using a Junction Field Effect Transistor (JFET) instead of a MOSFET. The JFET's inherent ability to handle high voltages (15-30 volts from the power amplifier) replaces the MOSFET's manufacturing advantage, as the JFET's depletion region structure provides superior voltage breakdown characteristics while still being fabricable in standard semiconductor processes.
3Manufacturing precision
If filters are added to remove harmonics, then signal purity is improved, but device complexity and insertion loss increase
Solution Approach 1:
The patent extracts the harmonic rejection function from separate filter circuits and integrates it directly into the switch device itself. The JFET's nonlinear capacitance characteristics and frequency-dependent impedance naturally attenuate harmonic frequencies, eliminating the need for additional external filters while maintaining signal purity and reducing overall device complexity.
4Power
If higher power is transmitted to improve communication range, then power output is improved, but parasitic leakage and harmonic interference worsen
Solution Approach 1:
The patent converts the JFET's nonlinear electrical characteristics, which could potentially generate harmonics, into a beneficial filtering mechanism. The device's inherent frequency-dependent impedance and capacitance variations naturally attenuate harmonic frequencies generated by the high-power amplifier, transforming what could be a harmful effect into a useful harmonic rejection feature without requiring additional active filtering components.
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 solution effectively reduces parasitic leakage and harmonic interference, achieving strong attenuation of frequencies above the primary frequency while maintaining minimal attenuation at the operating frequency, thus eliminating the need for filters to remove harmonics and ensuring the RF switch can handle high voltages.
Implementation Method 1
a first valve (300) configured to change an impedance of the first transmission line (210) and a second valve (300) configured to change an impedance of the second transmission line (220)
Data Source
AI summary
RF switching devices are provided that alternatively couple an antenna to either a transmitter amplifier or a receiver amplifier. An exemplary RF switching device comprises two valves, one for a receiver transmission line between the antenna and the receiver amplifier, the other for a transmitter transmission line between the antenna and the power amplifier. Each valve is switchably coupled between ground and its transmission line. When coupled to ground, current flowing through the valve increases the impedance of the transmission line thereby attenuating signals on the transmission line. When decoupled from ground, the impedance of the transmission line is essentially unaffected. The pair of valves is controlled such that when one valve is on the other valve is off, and vice versa, so that the antenna is either receiving signals from the power amplifier or the receiver amplifier is receiving signals from the antenna.