Output Driver Voltage Shifting for Low-Breakdown MOSFETs
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Solution Overview
Problem
As integrated circuits scale down, the oxide-breakdown voltage of MOSFETs reduces, leading to breakdown and failure of conventional output drivers that require a voltage swing exceeding the oxide-breakdown voltage, necessitating a solution to prevent transistor breakdown while maintaining compliance with output standards.
Innovation Solution
The implementation of source followers for voltage-level shifting and the use of LDMOS transistors to constrain voltages within safe limits, along with overvoltage protection circuitry and switching transistors to minimize crow-bar current, allows output drivers to operate with transistors having low oxide-breakdown voltage without breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional output drivers are used with scaled-down transistors, then circuit integration is improved, but transistor breakdown occurs due to voltage swing exceeding oxide-breakdown voltage
Solution Approach 1:
The patent introduces an intermediary voltage-level shifting circuit between the output driver and the load. This circuit acts as a mediator that transforms the high-voltage output signal into a low-voltage control signal suitable for the scaled-down transistors, preventing direct voltage stress on the gate oxide while maintaining the required output drive capability.
Solution Approach 2:
The patent changes the voltage parameters by implementing a voltage-level shifting mechanism that converts the output voltage from the original high level (exceeding oxide-breakdown voltage) to a lower level that is safe for the scaled transistors. This parameter transformation allows the system to maintain high output voltage swing capability while protecting the transistor gate oxide from breakdown.
2Reliability
If voltage-level shifting is implemented to protect transistors, then transistor reliability is improved, but device complexity increases
Solution Approach 1:
The voltage-level shifting circuit is designed to perform multiple functions: it protects the transistor gate oxide from high voltage, maintains the required output drive strength, and ensures compatibility with both high-voltage output requirements and low-voltage transistor operation. This multi-functionality reduces the need for separate protection circuits and simplifies the overall device architecture.
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 approach enables output drivers to achieve the required voltage swing while preventing transistor breakdown, ensuring reliable operation and compliance with standards like the USB 1.1 standard using MOSFETs with low oxide-breakdown voltage, reducing power dissipation and extending device lifespan.
Implementation Method 1
a first source follower coupled between the input node and the gate of the first output transistor and configured to prevent a source-to-gate voltage of the first output transistor from exceeding an oxide-breakdown voltage of the first output transistor
Implementation Method 2
a second source follower coupled between the input node and the gate of the second output transistor and configured to prevent a gate-to-source voltage of the second output transistor from exceeding the oxide-breakdown voltage
Data Source
AI summary
Aspects of the subject technology allow an output driver to be implemented using one or more transistors having an oxide-breakdown voltage below the output voltage swing of the output driver. The output driver can include one or more source followers, where a source follower provides voltage-level shifting of a voltage before the voltage is supplied to a gate of a transistor to prevent a source-to-gate voltage or a gate-to-source voltage of the transistor from exceeding the oxide-breakdown voltage of the transistor.