MOSFET RF Switch Gate Discharge Path for Lower Peak Current
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Solution Overview
Problem
MOSFET-based RF switches face challenges in achieving high voltage handling while maintaining low on-state resistance, leading to large load current peaks during switching transients, which can slow down the switching process or require more complex charge pumps.
Innovation Solution
Incorporating a discharge switch between the gate and drain-source resistive bias network, which establishes a current path only during the discharge phase of the switching transient, reducing peak load current and overall charge from the charge pump.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a high stack size (20-35 transistors) is used to achieve high voltage handling, then voltage handling capability is improved, but peak load current during switching transient increases
Solution Approach 1:
The gate bias network is segmented into multiple parallel paths: a high-ohmic path for steady-state biasing and a low-ohmic discharge path for transient charge removal. This segmentation allows the system to handle high voltages through the stacked transistor configuration while providing a dedicated low-resistance path that limits peak discharge current during switching transients.
Solution Approach 2:
A discharge switch is introduced as an intermediary component between the gate and the bias network. This discharge switch acts as a mediator that provides a controlled low-ohmic path during transients, enabling fast charge removal without subjecting the charge pump to excessive current peaks. The discharge switch is activated only during switching transients and remains inactive during steady-state operation.
2Device complexity
If a weak charge pump is used to meet steady-state current requirements, then charge pump complexity is reduced, but switching speed decreases due to inability to handle current peaks
Solution Approach 1:
The bias network is divided into two functional segments: a high-ohmic path that satisfies steady-state current requirements (allowing use of weak charge pumps) and a low-ohmic discharge path that handles transient current demands (enabling fast switching). This segmentation decouples the steady-state and transient requirements, allowing a simple charge pump to be used while still achieving fast switching through the discharge path.
Solution Approach 2:
The discharge path is pre-configured and ready to activate during switching transients. By having the low-ohmic discharge path prepared in advance (through the discharge switch), the system can rapidly remove gate charge during transients without relying on the charge pump's continuous current capability, thus enabling fast switching with a simple charge pump.
3Use of energy by moving object
If high-ohmic resistors are used for biasing, then steady-state current consumption is reduced, but discharge time constant increases slowing down switching
Solution Approach 1:
The bias network is segmented into parallel paths with different resistance values: a high-ohmic path for steady-state biasing (reducing continuous power consumption) and a low-ohmic discharge path for transient charge removal (reducing discharge time). The discharge switch controls which path is active, allowing the system to optimize for either low power or fast switching as needed.
Solution Approach 2:
The bias network transitions from a static high-ohmic configuration to a dynamic configuration where the discharge switch can temporarily switch in a low-ohmic path. This dynamic adjustment allows the system to have high resistance during steady-state (low power consumption) and low resistance during transients (fast discharge), effectively resolving the contradiction between power consumption and switching speed.
Data Source
AI summary
An RF switch device includes transistors coupled in series to form a current path; a drain-source resistive bias network coupled to a drain and a source of each transistor; and a discharge switch coupled between a gate of at least one transistor and the drain-source resistive bias network, wherein the discharge switch establishes a current path between the gate of the at least one transistor and the drain-source resistive bias network only during a switching transient of the RF switch device.