RF Switch Chain Biasing for Uniform Voltage and Lower Harmonics
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Solution Overview
Problem
Existing radio frequency switch circuits face issues with voltage nonuniformity and harmonic deterioration due to high voltage swings, particularly in multi-standard communication systems, which affect antenna performance and efficiency.
Innovation Solution
A radio frequency switch circuit design that includes a switch chain with MOS transistors connected to bias circuits through T-shaped resistance networks and capacitors, optimizing voltage distribution and reducing harmonics by adjusting parasitic capacitance and transistor sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the voltage withstood by each switch unit is increased to handle higher voltage swings, then the voltage handling capability of the switch circuit is improved, but the harmonics generated by the switch units deteriorate
Solution Approach 1:
The switch circuit is divided into multiple switch units connected in series, where each unit withstands a portion of the total voltage swing. This segmentation allows the circuit to handle higher voltages while keeping the voltage stress on each individual unit manageable, thereby reducing harmonic generation.
Solution Approach 2:
Different bias voltages are applied to different switch units based on their local voltage swing requirements. The bias circuit adjusts the operating point of each switch unit individually, optimizing performance for its specific voltage conditions and minimizing harmonic distortion.
2Strength
If the quantity of switch units is increased to withstand higher voltages, then the voltage handling capability is improved, but the device complexity increases
Solution Approach 1:
Multiple switch units are combined in a series configuration within a single integrated circuit chip, sharing common biasing and control structures. This merging approach achieves high voltage handling capability while minimizing the increase in overall device complexity through shared resources.
Solution Approach 2:
The bias circuit is designed to serve multiple switch units simultaneously, providing universal voltage distribution and control functions. This multi-functional bias circuit reduces the need for separate control mechanisms for each switch unit, thereby limiting complexity growth.
3Strength
If the voltage swing withstood by the switch is increased, then the voltage handling capability is improved, but the harmonics rise in a cliff-like manner
Solution Approach 1:
Bias voltages are pre-applied to each switch unit before the RF signal arrives, establishing optimal operating points that preemptively prepare the switches to handle upcoming voltage swings. This preliminary biasing ensures smooth operation and prevents sudden harmonic spikes when voltage swings increase.
Solution Approach 2:
The bias voltages applied to different switch units are dynamically adjusted based on their position in the voltage swing profile. By changing the bias parameters locally, the circuit maintains optimal operation across the entire voltage range, preventing cliff-like harmonic increases.
Data Source
AI summary
Disclosed are a radio frequency switch circuit, a chip, and a communication terminal. In the radio frequency switch circuit, a switch chain is formed by at least one switch unit being provided between a first port and a second port; each switch unit is connected to a first bias circuit and to a second bias circuit; further adjustments are made to the ratio of the parasitic capacitance between MOS transistors of each switch unit to a third capacitance; and adjustments are made to the size of said MOS transistors as well as to the ratio of said size to the third capacitance. In this way, voltage distribution uniformity on the switch chain may be improved, thus increasing the overall voltage withstand ability of the radio frequency switch circuit, and reducing the occurrence of harmonic events.