Data Communication Driver Circuit With Voltage-Relaxing MOSFET Protection
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Solution Overview
Problem
Data communication circuits face breakdown issues due to low breakdown voltage, particularly with the second nMOS transistor when no power supply voltage is applied to its gate, leading to excessive inter-terminal voltage and potential transistor breakdown.
Innovation Solution
Incorporating voltage-relaxing transistors with specific configurations, including auxiliary transistors and a voltage adjustment section, to manage and reduce inter-terminal voltages, ensuring they remain below breakdown levels, and using threshold voltages that exceed maximum voltage differences to prevent breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a voltage-relaxing transistor is added to protect the driver from breakdown, then the driver protection is improved, but the device complexity increases
Solution Approach 1:
A voltage-relaxing transistor is introduced as an intermediary component between the driver and the signal line. This transistor acts as a mediator that relaxes the voltage stress on the driver by providing a controlled path for voltage dissipation, thereby protecting the driver from breakdown while maintaining circuit functionality.
Solution Approach 2:
The voltage-relaxing transistor is configured to provide beforehand cushioning by establishing a protective mechanism before voltage breakdown can occur. The transistor's gate is connected to detect voltage conditions, and when excessive voltage is detected, the transistor activates to clamp or relax the voltage, preventing breakdown of the driver in advance.
2Device complexity
If the gate of the second nMOS transistor is left floating (no power supply voltage applied), then the circuit simplicity is improved, but the transistor breakdown risk increases
Solution Approach 1:
The voltage-relaxing transistor serves as an intermediary that protects the second nMOS transistor even when its gate is left floating. By connecting the gate of the voltage-relaxing transistor to the signal line, the system ensures that the voltage-relaxing transistor can detect and respond to voltage conditions, activating its protective function without requiring a dedicated power supply connection to the second transistor's gate.
Solution Approach 2:
The voltage-relaxing transistor is configured to provide self-service protection by using the signal line voltage itself to control its operation. The gate of the voltage-relaxing transistor is connected to the signal line, allowing it to automatically detect voltage conditions and activate its protective function without external control signals or additional power supply connections.
3Reliability
If voltage-relaxing transistors are used to protect both driver and transistor, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The voltage-relaxing transistor is designed with multi-functionality to serve dual protective roles. By configuring the transistor with its source connected to the driver supply node, drain connected to the signal node, and gate connected to the complementary signal node, it simultaneously protects both the driver from voltage breakdown and the transistor itself from inter-terminal voltage breakdown, eliminating the need for separate protection circuits.
Solution Approach 2:
The protective functions for both the driver and the voltage-relaxing transistor are merged into a single integrated configuration. The voltage-relaxing transistor is positioned and wired such that it provides a unified protection mechanism that addresses both protection needs simultaneously, reducing the overall device complexity compared to using separate protection circuits for each component.
Data Source
AI summary
A driver supplies data signal via a supply node. A voltage-relaxing transistor has a source connected to the supply node of the driver, a drain connected to a signal node connected to a signal line, and a gate to which the voltage at the signal node is applied.