GaN Power Transistor Current Sensing With Drain-Voltage Feedback
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Solution Overview
Problem
Existing current sensing devices in GaN HEMTs face challenges in achieving a balance between sensitivity and accuracy due to temperature variations, dynamic on-state resistance, and manufacturing process variations, leading to non-linear current sensing signals.
Innovation Solution
A feedback circuit is implemented to maintain the sensing transistor at the same voltage level as the main power transistor, using an operational amplifier and transconductor to create a feedback loop, ensuring identical operational conditions and scaling the sensing transistor to a smaller area, with a switching circuit to disconnect the feedback during high voltage states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high Vcs signal is used to increase sensitivity, then the sensitivity of the device is improved, but the linearity of the current sensing signal deteriorates
Solution Approach 1:
The patent implements a feedback circuit that includes an operational amplifier and a transconductor. The operational amplifier amplifies the voltage difference between the main drain and sensing transistor drain, and the transconductor converts this voltage signal to a current that feeds back to the sensing transistor drain. This feedback mechanism maintains the voltage across the sensing transistor at a constant level, ensuring linear current sensing while preserving sensitivity through the amplification stage.
2Measurement precision
If the current through the sensing transistor is increased to improve sensitivity, then the sensitivity is improved, but the accuracy with respect to temperature variations deteriorates
Solution Approach 1:
The feedback circuit maintains the drain voltage of the sensing transistor equal to the drain voltage of the main power transistor by using the operational amplifier to detect voltage differences and the transconductor to provide compensating current. This equipotential condition ensures that both transistors operate under identical voltage conditions, making the current ratio independent of temperature variations and improving accuracy while maintaining sensitivity.
3Measurement precision
If a sensing transistor with larger area is used to increase sensitivity, then the sensitivity is improved, but the device complexity increases
Solution Approach 1:
The patent changes the operational parameters of the sensing transistor by introducing the feedback circuit that controls the drain voltage. Instead of increasing the transistor area to improve sensitivity, the feedback mechanism adjusts the voltage parameter to maintain optimal operating conditions. This approach improves sensitivity without requiring larger device areas, thereby avoiding increased device complexity.
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
The solution enhances the linearity and accuracy of current sensing across varying conditions, including temperature and process variations, while maintaining high sensitivity and immunity to dynamic on-state resistance changes.
Implementation Method 1
A feedback circuit is implemented to maintain the sensing transistor at the same voltage level as the main power transistor, using an operational amplifier and transconductor to create a feedback loop
Implementation Method 2
The use of an Aluminium Galium Nitride (AlGaN)/GaN heterostructure also allows the formation of a two-dimensional electron gas (2DEG) at the hetero-interface where carriers can reach very high mobility (μ=2000 cm2/(Vs)) values
Implementation Method 3
the piezopolarization charge present at the AlGaN/GaN heterostructure, results in a high electron density in the 2DEG layer (e.g. 1e13 cm−2)
Data Source
AI summary
According to a first aspect of the disclosure, there is provided an electronic device comprising: a power device circuit comprising: (i) a main power transistor, comprising a main drain terminal, a main source terminal and a main gate terminal, (ii) a resistive sensing load, and (iii) a sensing transistor comprising a source connected to the main source terminal, a gate connected to the main gate terminal and a drain connected to a first terminal of the resistive sensing load. The electronic device further comprises: a feedback circuit comprising at least one operational amplifier and at least one transconductor, and a switching circuit comprising at least one switch for connecting and disconnecting the power device circuit to the feedback circuit. A first input of the at least one operational amplifier and a second terminal of the resistive sensing load are selectively connected to the main drain terminal through the switching circuit. A second input of the at least one operational amplifier and at least one output of the at least one transconductor are selectively connected to the drain of the sensing transistor through the switching circuit. The main power transistor has a first area or gate perimeter and the sensing transistor has a second area or gate perimeter smaller than the first area or gate perimeter. During an ON state of the main power transistor, the output current of the transconductor of the feedback circuit is proportional to the potential difference between the main drain terminal and the drain of the sensing transistor, resulting in a voltage across the resistive sensing load of substantially zero.