RF Switch Cells With Bias-Free Varactors for Harmonic Control
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Solution Overview
Problem
Traditional off-state linearization networks for RF switches require external bias circuitry, occupying valuable circuit real estate and generating undesirable harmonics due to non-linear capacitance, which interfere with RF transceiver receiver circuitry.
Innovation Solution
The implementation of radio frequency switches with off-state linearization networks that utilize varactors, specifically inversion-mode and accumulation-mode varactors, which are tuned without external bias, reducing harmonic distortion by counteracting parasitic non-linear capacitances inherent in the RF switch cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a traditional off-state linearization network is placed in parallel with the RF switch to reduce harmonic distortion, then the harmonic distortion is reduced, but the circuit occupies more real estate and requires external bias circuitry
Solution Approach 1:
The patent combines the off-state linearization network with the RF switch cell structure by integrating varactors directly into the switch cell, sharing common nodes and eliminating the need for separate external bias circuitry. This merging approach reduces the overall circuit footprint while maintaining harmonic distortion reduction functionality.
Solution Approach 2:
The integrated varactors are controlled by the existing gate voltage applied to the FET for switching operation. The same gate voltage that controls the switch state also controls the varactor capacitance, eliminating the need for separate external bias circuitry and making the system self-sufficient.
2Object-affected harmful factors
If the RF switch is kept in off-state to block transmit signals, then signal isolation is achieved, but non-linear capacitance generates undesirable harmonics that interfere with receiver circuitry
Solution Approach 1:
The varactors are configured to provide preliminary compensation for the non-linear capacitance effects before they can generate significant harmonics. By anticipating and counteracting the non-linear behavior through pre-biased varactor capacitance, the system reduces harmonic generation while maintaining signal isolation in the off-state.
Solution Approach 2:
The patent changes the capacitance parameter of the switch cell by introducing voltage-controlled varactors. By dynamically adjusting the varactor capacitance based on the gate voltage, the system modifies the overall capacitance characteristic to reduce non-linearity and harmonic generation while maintaining the off-state isolation function.
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 harmonic distortion without the need for external bias circuitry, enhancing circuit efficiency and minimizing interference with RF transceiver receiver circuitry, while maintaining or improving the figure of merit of RF switches.
Implementation Method 1
The off-state linearization network includes varactors coupled to the drain terminal and the source terminal of the field-effect transistor
Data Source
AI summary
A radio frequency switch having a first node, a second node, and a plurality of switch cells that are coupled in series between the first node and the second node is disclosed. Each of the plurality of switch cells includes a field-effect transistor having a drain terminal, a source terminal, a FET gate terminal, and a body terminal and an off-state linearization network. The off-state linearization network includes varactors coupled to the drain terminal and the source terminal of the field-effect transistor.