GaN Gate Driver Active Pre-Driver With Feedback for Fast Turn-On
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Solution Overview
Problem
Conventional bootstrapping gate drivers and active pre-drivers for enhancement mode GaN FETs face issues with high power consumption and increased complexity due to noise from the supply voltage and the need for multiple supply voltages, which affects their efficiency and area usage.
Innovation Solution
An active pre-driver with feedback that operates on a single, higher supply voltage, using a current source and feedback circuit to maintain a lower output voltage, reducing power consumption and complexity by quickly turning on the output stage pull-up FET and incorporating a cascode current mirror or depletion mode transistor for efficient current management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a bootstrapping gate driver is used to provide increased voltage to the gate terminal, then the gate voltage is maintained above supply voltage, but noise from the supply voltage appears directly in the output voltage and power consumption increases
Solution Approach 1:
The patent introduces an intermediary feedback circuit that senses the output voltage and controls the pre-driver transistor to regulate the voltage at the gate terminal. This feedback mechanism acts as a mediator between the supply voltage and the gate terminal, preventing direct coupling of supply noise while maintaining the required gate voltage levels.
Solution Approach 2:
The patent implements a feedback circuit that monitors the output voltage and adjusts the pre-driver transistor gate voltage accordingly. This feedback loop ensures that the gate terminal maintains the necessary voltage above supply voltage while the feedback regulation prevents supply noise from appearing directly at the output, resolving the contradiction between high gate voltage and noise rejection.
2Speed
If an active pre-driver with depletion mode transistors is used to supply additional drive current, then turn-on speed is improved, but the circuit complexity and area increase
Solution Approach 1:
The patent employs enhancement mode GaN FETs to perform multiple functions: they act as both the main output transistors and the pre-driver transistors. This multi-functionality eliminates the need for separate depletion mode transistors, reducing circuit complexity and device area while maintaining the fast turn-on performance provided by the active pre-driver configuration.
Solution Approach 2:
The patent changes the operating parameters of enhancement mode GaN FETs by using feedback control to dynamically adjust their gate voltages. This allows the enhancement mode devices to operate in regions that provide both fast switching and efficient current supply, achieving the performance previously requiring depletion mode transistors without the associated complexity.
3Strength
If multiple supply voltages are used to operate the gate driver, then the gate terminal can be driven to higher voltages, but the area and complexity of the driver circuit increase
Solution Approach 1:
The patent uses a feedback circuit to dynamically control the pre-driver transistor, enabling the gate terminal to reach voltages above the supply voltage without requiring multiple supply voltage sources. The feedback mechanism ensures proper voltage regulation while operating from a single supply, reducing the area and complexity associated with multiple voltage rails.
Solution Approach 2:
The gate driver circuit uses its own supply voltage to generate the necessary gate drive voltages through the feedback-controlled pre-driver configuration. The circuit essentially serves itself by using the available supply voltage in combination with feedback control to create the required voltage conditions, eliminating the need for additional dedicated high-voltage supply sources.
Data Source
AI summary
An enhancement mode GaN FET based gate driver circuit including an active pre-driver to drive a high-slew rate, high current output stage GaN FET. Due to the active driver current from the pre-driver, the output stage pull-up FET can turn on faster as compared to a pre-driver that utilizes a passive pull-up load. The active pre-driver must provide a voltage to drive the gate of the output stage pull-up FET which is higher than the normal supply voltage to enable the maximum output level of the driver FET to approach the normal supply voltage. A feedback circuit is included in the active pre-driver to avoid the need for two supply voltages.