Stacked FET Switch Biasing Without Negative Gate Voltage
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Solution Overview
Problem
Existing stacked FET switches require complex control circuits with negative voltage generators and excessive bias swings, which add complexity and can cause issues during transitions, and often necessitate negative body biasing to prevent reverse bias diodes from activating, leading to poor linearity in floating body designs.
Innovation Solution
A stacked FET switch design that biases gate contacts at a positive voltage relative to ground during the closed state and at a lower non-negative voltage during the open state, eliminating the need for negative biasing and reducing bias swings, thereby simplifying the control circuit and preventing FET devices from being turned on without a negative gate bias.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If negative voltage generators are used to bias gate contacts during open state, then FET devices can be kept off during open state, but control circuit complexity increases
Solution Approach 1:
The patent extracts and eliminates the negative voltage generator from the control circuit. Instead of using active negative voltage generation, the invention uses a simplified biasing scheme where the gate is biased at a negative voltage relative to the source during the open state, but this is achieved through passive means (bias networks) rather than active negative voltage generators, thereby reducing circuit complexity while maintaining reliable off-state operation.
Solution Approach 2:
The patent inverts the traditional biasing approach by making the source the reference point rather than ground. The gate is biased at a negative voltage relative to the source, and the drain is biased at a positive voltage relative to the source. This inversion of the reference point eliminates the need for symmetric positive and negative voltage generators, simplifying the control circuit.
2Reliability
If excessive bias swings are used to switch FET states, then FET can be reliably switched between open and closed states, but transition issues and reliability problems occur
Solution Approach 1:
The patent changes the biasing parameters to eliminate excessive voltage swings. By biasing the gate at a negative voltage relative to the source during the open state and at a positive voltage relative to the source during the closed state, the gate-to-source voltage swing is reduced. Additionally, by properly biasing the drain and source voltages, the gate-to-drain voltage swing is minimized, preventing breakdown and improving transition reliability.
3Reliability
If negative body biasing is applied to prevent reverse bias diode activation, then diode activation is prevented, but linearity deteriorates in floating body designs
Solution Approach 1:
The patent applies local quality by independently controlling the body voltage separately from the gate and drain voltages. The body is biased at a voltage that is negative relative to the drain during the open state to prevent reverse bias diode activation, but this localized body biasing does not deteriorate linearity because it is applied specifically to the body region rather than affecting the entire device operation. This localized control allows prevention of diode activation while maintaining floating body advantages.
Data Source
AI summary
Described are embodiments of stacked field effect transistor (FET) switch having a plurality of FET devices coupled in series to form an FET device stack. A control circuit provides biasing voltages to the gate, source, and drain contacts of each of the plurality of FET devices to switch the FET device stack to and from a closed state and an open state. In the open state, the gate contacts of each of the plurality of FET devices are biased by the control circuit at the second voltage. To prevent activation in the open state, the control circuit biases the drain contacts and source contacts of each of the plurality of FET devices at the first voltage. The first voltage is positive relative to a reference voltage, such as ground, while the second voltage is non-negative relative to the reference voltage but less than the first voltage.