Bi-Directional Transistor Body Biasing Against Snapback
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Bi-directional transistors are sensitive to current and voltage rates during fast turn-off, leading to potential snapback of output I-V characteristics and premature device destruction due to non-uniform body resistance and bipolar triggering, which affects their blocking voltage and reliability.
Innovation Solution
Incorporating a negative-voltage-source, such as a charge pump, between the body and source terminals to provide reverse biasing, which reduces the impact of non-uniform body resistance and improves the robustness of the bi-directional transistor by increasing the body-source barrier and preventing premature triggering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If fast turn-off is implemented in bi-directional transistor, then switching speed is improved, but bipolar triggering and snapback occur leading to device destruction
Solution Approach 1:
The patent applies preliminary anti-action by pre-charging the body terminal to a positive voltage (VBODY = VCC/2) before the fast turn-off event. This pre-established positive body voltage creates a potential barrier that prevents bipolar triggering and snapback during the subsequent fast switching operation, thereby allowing high switching speed without compromising device reliability
Solution Approach 2:
The patent implements preliminary action through a precharge transistor that charges the body terminal to VCC/2 before the main switching operation. This preliminary charging action establishes the necessary voltage condition (VBODY > 0) that prevents harmful bipolar effects during fast turn-off, enabling both high speed and reliable operation
2Device complexity
If body terminal is held at ground potential, then circuit simplicity is maintained, but non-uniform body resistance causes premature triggering
Solution Approach 1:
The patent changes the body terminal voltage parameter from ground (0V) to a positive voltage (VCC/2). This parameter change transforms the body resistance characteristics, ensuring uniform potential distribution across the body terminal during blocking operation, thereby preventing premature bipolar triggering while maintaining acceptable circuit complexity through simple voltage sourcing
3Reliability
If negative voltage bias is applied to body terminal, then bipolar triggering is prevented, but additional voltage source complexity is introduced
Solution Approach 1:
The patent inverts the conventional approach by applying positive voltage (VCC/2) to the body terminal instead of negative voltage. This inversion achieves the same protective effect against bipolar triggering while utilizing readily available positive voltage rails from the power supply, thereby reducing voltage source complexity compared to dedicated negative voltage generation circuits
Solution Approach 2:
The patent employs the existing VCC power rail to serve multiple functions: it provides the precharge voltage for the body terminal, maintains the potential barrier during blocking, and supports the overall circuit operation. This multi-functional use of the positive voltage rail eliminates the need for separate negative voltage sources, reducing overall circuit complexity
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
The negative-voltage-source effectively enhances the bi-directional transistor's ability to sustain high dV/dt without bipolar triggering, improving its robustness and performance by maintaining a higher potential barrier between the source and drain, thus preventing current focalization and device destruction.
Implementation Method 1
Incorporating a negative-voltage-source, such as a charge pump, between the body and source terminals to provide reverse biasing, which reduces the impact of non-uniform body resistance and improves the robustness of the bi-directional transistor by increasing the body-source barrier
Data Source
Figure 1~3
Figure 4
Figure 5~7
AI summary
A body-control-device for a bi-directional transistor, said bi-directional transistor having a first-transistor-channel-terminal, a second-transistor-channel-terminal, a transistor-control-terminal and a transistor-body-terminal. The body-control-device comprises a body-control-terminal connectable to the transistor-body-terminal of the bi-directional transistor, a first-body-channel-terminal connectable to the first-transistor-channel-terminal of the bi-directional transistor, a second-body-channel-terminal connectable to the second-transistor-channel-terminal of the bi-directional transistor, a negative-voltage-source and a switching-circuit configured to selectively provide an offset-first-circuit-path between the first-body-channel-terminal and the body-control-terminal, wherein the offset-first-circuit-path includes the negative-voltage-source such that it provides a negative voltage bias between the body-control-terminal and the first-body-channel-terminal.