RF Switch Driver Impedance Control for Low-Loss Voltage Stacking
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Solution Overview
Problem
RF switches face challenges in handling large voltage swings and managing parasitic capacitances, which can attenuate and degrade RF signals, especially as components become more integrated in fine geometry processes.
Innovation Solution
The implementation of a radio frequency (RF) switching circuit with series connected RF switch cells and a switch driver that varies impedance based on the control node voltage, using low impedance during transitions and high impedance in settled states to reduce parasitic capacitances and ensure fast transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If large devices are used to withstand higher voltages, then voltage handling capability is improved, but parasitic capacitances increase which attenuate and degrade RF signals
Solution Approach 1:
The patent divides the RF switch into multiple series-connected switch cells, where each cell uses smaller transistors that can withstand lower individual voltages. By stacking these cells in series, the circuit achieves both high voltage handling capability and reduced parasitic capacitance per cell, resolving the contradiction between strength and harmful factors.
2Strength
If more series connected switch cells are used, then voltage handling capability is improved, but insertion loss increases due to cumulative parasitic effects
Solution Approach 1:
The patent employs a variable impedance driver that dynamically adjusts its output impedance based on the switching state. During transitions, the driver provides low impedance to quickly charge/discharge gate capacitances and reduce transition time. In settled states, it provides high impedance to minimize parasitic loading and reduce insertion loss, thus resolving the contradiction between strength and energy loss.
Solution Approach 2:
The driver circuit changes its output impedance parameter dynamically - using low impedance during switching transitions to minimize transition time and high impedance during settled states to minimize parasitic loading. This parameter change approach reduces cumulative parasitic effects in multi-cell configurations while maintaining voltage handling capability.
3Productivity
If faster switching transitions are implemented, then productivity is improved, but parasitic capacitances have more time to affect the signal
Solution Approach 1:
The variable impedance driver dynamically switches between low impedance during transitions (enabling fast switching by providing strong drive current to charge/discharge parasitic capacitances quickly) and high impedance in settled states (minimizing parasitic loading). This dynamic approach resolves the contradiction between productivity and harmful factors by optimizing impedance at different times.
Data Source
AI summary
In accordance with an embodiment, a radio frequency (RF) switching circuit includes a plurality of series connected RF switch cells having a load path and a control node, and a switch driver coupled to the control node. Each of the plurality of series connected RF switch cells includes a switch transistor and a gate resistor having a first end coupled to a gate of the switch transistor and a second end coupled to the control node. The switch driver includes a variable output impedance that varies with a voltage of the control node.