Passive Substrate Discharge Circuit for Bidirectional Switches
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Solution Overview
Problem
Conventional bidirectional switches with a common substrate face performance degradation due to uncontrolled substrate voltage during switching, as back-to-back diodes fail to maintain the substrate at a desired voltage, leading to negative potential confinement and parasitic capacitive coupling issues.
Innovation Solution
A passive substrate voltage discharge circuit is integrated with the bidirectional switch, utilizing normally-on switches in anti-series configuration with the substrate as a midpoint, and passive voltage clamping devices to discharge substrate voltage effectively in both directions, eliminating the need for additional gate drivers or control components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If back-to-back diodes are integrated to provide a discharge path for the substrate, then a discharge path is provided, but the substrate voltage is not held close to 0V during on-state due to negative charge confinement
Solution Approach 1:
The patent inverts the conventional approach by using normally-on switches instead of diodes, and by configuring them in anti-series rather than back-to-back. This inversion allows the substrate voltage to be held close to 0V during on-state by providing a low-impedance discharge path through the normally-on switches, preventing negative charge confinement that occurs with diode-based solutions.
Solution Approach 2:
The patent changes the operational state parameter of the switches from normally-off (conventional MOSFETs) to normally-on. This parameter change enables the substrate discharge circuit to be active during on-state, continuously maintaining substrate voltage near 0V. The normally-on characteristic ensures the discharge path remains conductive when the bidirectional switch is on, preventing voltage drift.
2Device complexity
If the substrate is kept floating with one source biased at high voltage, then the configuration is simplified, but the substrate experiences large negative potential during on-state degrading device performance
Solution Approach 1:
The patent introduces an intermediary substrate discharge circuit consisting of normally-on switches connected between the substrate and the input-output terminals. This intermediary circuit acts as a mediator that actively manages substrate voltage, providing a controlled discharge path for negative charges while maintaining the simplified floating substrate configuration. The normally-on switches serve as the intermediary element that reconciles the simplified configuration with performance requirements.
3Adaptability or versatility
If two separate gates with common drain are used in monolithic device, then bidirectional switching capability is achieved, but source connection to substrate is not possible requiring floating substrate
Solution Approach 1:
The patent makes the normally-on switches multi-functional by integrating them into the same monolithic device structure as the bidirectional switch. These switches serve dual purposes: they provide the necessary substrate discharge path while maintaining the bidirectional switching capability. The common source configuration of the normally-on switches allows them to function both as discharge elements and as part of the overall switching architecture, eliminating the need for separate substrate connection circuits.
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
This solution maintains the substrate voltage near zero volts during the on-state, preventing voltage variations across parasitic capacitances and enhancing switching behavior by redistributing stored charges through a voltage divider, thus improving the overall performance of the bidirectional switch.
Implementation Method 1
The passive substrate voltage discharge circuit effectively stabilizes the substrate voltage, preventing voltage fluctuations and maintaining optimal switching performance by redistributing stored charge through a voltage divider
Implementation Method 2
a passive substrate voltage discharge circuit in parallel with the bidirectional switch and configured to discharge a voltage of the substrate region in both directions of the bidirectional switch
Implementation Method 3
passive voltage clamping devices to maintain substrate voltage at a desired level
Data Source
AI summary
A semiconductor device includes a semiconductor body having an active region and a substrate region that is disposed beneath the active region, and a bidirectional switch formed in the semiconductor body. The bidirectional switch includes first and second gate structures that are each configured to control a conductive state of an electrically conductive channel that is disposed in the active region, and first and second input-output terminals that are each in ohmic contact with the electrically conductive channel. A passive substrate voltage discharge circuit in parallel with the bidirectional switch is configured to discharge a voltage of the substrate region in both directions of the bidirectional switch. The passive substrate voltage discharge circuit includes first and second normally-on switches connected in anti-series between the first and second input-output terminals in a common source configuration with the substrate region as a midpoint.