Passive Substrate Discharge Circuit for Bidirectional Switches
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Solution Overview
Problem
Conventional bidirectional switches with a common drain configuration face performance degradation due to the inability to maintain the substrate voltage close to 0V during the on-state, leading to large negative potentials and inefficient switching behavior.
Innovation Solution
A passive discharge circuit is integrated with the bidirectional switch, providing a discharge path for the substrate and voltage blocking capabilities without requiring additional gate drivers or control components, utilizing a combination of normally-on and normally-off devices to manage substrate potential.
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, causing large negative potentials and performance degradation
Solution Approach 1:
The discharge circuit is segmented into multiple components: a first discharge device (first normally-off HEMT) connected to the first source, a second discharge device (second normally-off HEMT) connected to the second source, and a control device. Each segment operates independently to manage substrate voltage during different switching states, resolving the contradiction between off-state protection and on-state voltage control.
Solution Approach 2:
The discharge circuit dynamically switches between different operational modes based on the bidirectional switch state. During off-state, the normally-on HEMTs provide substrate protection. During on-state, the control device activates the normally-off HEMTs to discharge substrate voltage, maintaining it close to 0V. This dynamic adaptation resolves the static limitation of back-to-back diodes.
2Device complexity
If the substrate is kept floating with one source biased at high voltage, then the configuration simplifies the circuit structure, but the substrate experiences large negative potential during on-state, degrading device performance
Solution Approach 1:
The discharge circuit uses the existing voltage differences during switching operations to automatically activate the appropriate discharge paths. The control device monitors substrate voltage and autonomously activates normally-off HEMTs when needed, without requiring external intervention. This self-service mechanism maintains performance stability without adding complex control circuitry.
3Ease of operation
If a passive discharge circuit is added to provide substrate discharge path, then substrate voltage is maintained close to 0V during on-state, but the device complexity increases
Solution Approach 1:
The passive discharge circuit components serve multiple functions: the first and second normally-off HEMTs provide substrate voltage discharge during on-state, the normally-on HEMTs provide protection during off-state, and the control device manages both discharge paths. This multi-functionality reduces the need for separate dedicated circuits for each function, minimizing overall complexity while achieving both voltage control and protection.
Data Source
AI summary
A semiconductor device includes: a semiconductor body having an active region and a substrate region beneath the active region; a bidirectional switch having first and second gate structures configured to control a conductive state of a channel in the active region, and first and second input-output terminals electrically connected to the channel; and a passive discharge circuit in parallel with the bidirectional switch and configured to utilize a fraction of a voltage across the first and second input-output terminals to switch on a transistor device that electrically connects the substrate region to the input-output terminal at the lower potential during an off-state of the bidirectional switch and during ZVS (zero-voltage switching) transition periods.