Bidirectional Switch Discharge Circuit for Substrate Voltage Stability
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Solution Overview
Problem
Conventional bi-directional switches with a common drain configuration face performance degradation due to the inability to effectively hold the substrate voltage close to 0V during the on-state, leading to large negative potential excursions during off-to-on switching, as the substrate lacks a reliable discharge path.
Innovation Solution
A semiconductor device incorporating a main bi-directional switch and a monolithically integrated discharge circuit with individual transistors or an auxiliary bi-directional switch, connected in a common source configuration, provides a passive discharge path for the semiconductor substrate, ensuring it remains at a desired voltage during the on-state without additional gate drivers or control components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If back-to-back diodes are integrated with anodes connected to the substrate, then the substrate is protected during off-state, but the substrate voltage cannot be held close to 0V during on-state and large negative potential occurs
Solution Approach 1:
The discharge function is segmented from the main bi-directional switch and implemented as a separate auxiliary bi-directional switch or individual transistors. This segmentation allows the discharge circuit to operate independently with passive gate control, effectively managing substrate voltage without interfering with the main switch operation.
Solution Approach 2:
The auxiliary bi-directional switch or individual transistors act as intermediary elements between the substrate and the main switch sources. These intermediary components provide a controlled discharge path that mediates the substrate voltage, preventing large negative potential excursions while maintaining the protective function during off-state.
2Stability of the object's composition
If a discharge path is added to the substrate, then substrate voltage is stabilized during on-state, but device complexity increases
Solution Approach 1:
The discharge circuit is merged with the main bi-directional switch to form an integrated monolithic device. The auxiliary bi-directional switch or individual transistors are combined with the main switch structures, sharing common substrates and fabrication processes, which minimizes the increase in device complexity while achieving effective substrate voltage stabilization.
Solution Approach 2:
The discharge circuit is designed with passive gate control that automatically activates based on the state of the main bi-directional switch. The gates are decoupled from external gate drive circuitry and controlled inherently by the voltage conditions, allowing the discharge function to self-regulate substrate voltage without requiring additional control components or complex gate drive circuits.
3Device complexity
If auxiliary switch with passive gate control is used, then gate drive circuitry is simplified, but control precision over discharge timing is reduced
Solution Approach 1:
The passive gate control mechanism dynamically responds to voltage conditions across the main switch sources. As the main switch transitions between states, the voltage differential automatically modulates the gate-to-source voltage of the auxiliary switch, enabling timely discharge activation without requiring precise external timing control. The system adapts its discharge timing based on real-time electrical conditions.
Data Source
AI summary
A semiconductor device includes a main bi-directional switch formed on a semiconductor substrate and having first and second gates, a first source electrically connected to a first voltage terminal, a second source electrically connected to a second voltage terminal, and a common drain. The semiconductor device further includes a discharge circuit having a plurality of individual transistors or an auxiliary bi-directional switch monolithically integrated with the main bi-directional switch and connected in a common source configuration to the semiconductor substrate. The plurality of individual transistors or the auxiliary bi-directional switch includes a first drain connected to the first source of the main bi-directional switch, a second drain connected to the second source of the main bi-directional switch, and first and second gates each decoupled from gate drive circuitry so that the first and the second gates are controlled at least passively and based on a state of the main bi-directional switch.