Temperature-Compensated NMOS Driving Circuit for Stable On-Resistance
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Solution Overview
Problem
Conventional driving circuits face challenges in maintaining a fixed overdrive voltage and turned-on resistance value of driving transistors, as these parameters vary with temperature due to changes in threshold voltage, affecting the stability of the driving voltage in circuit systems.
Innovation Solution
The proposed driving circuit incorporates a current source with a positive temperature coefficient and a predetermined resistance value to compensate voltage differences, ensuring the overdrive voltage and turned-on resistance value of the driving transistor remain independent of temperature variations, using a combination of NMOS and PNP/PMOS transistors and resistors to stabilize the output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a series of MOS transistors with connecting diodes are added to the gate end and source end of the driving transistor, then the overdrive voltage variation is reduced, but the overdrive voltage still changes with temperature variation
Solution Approach 1:
The patent changes the parameter of current temperature coefficient from negative to positive by using a PNP transistor instead of an NMOS transistor in the current source circuit. This positive temperature coefficient current compensates for the threshold voltage changes of the driving transistor, maintaining stable overdrive voltage across temperature variations.
Solution Approach 2:
The patent introduces a PNP transistor as an intermediary element in the current source circuit. This PNP transistor acts as a mediator that generates a positive temperature coefficient current, which compensates for the temperature-dependent threshold voltage changes of the driving transistor, thereby stabilizing the overdrive voltage.
2Reliability
If the overdrive voltage is maintained fixed to reduce turned-on resistance variation, then the turned-on resistance stability improves, but the circuit complexity increases due to additional transistors and diodes
Solution Approach 1:
The patent makes the current source circuit serve multiple functions: it provides the gate drive current for the driving transistor while simultaneously generating a positive temperature coefficient current for compensation. The PNP transistor-based current source replaces the need for separate compensation circuits, reducing overall device complexity while maintaining reliability.
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 solution provides a stable driving voltage for loads in circuit systems by making the overdrive voltage and turned-on resistance value of the driving transistor independent of temperature, thereby ensuring consistent performance across varying temperatures.
Implementation Method 1
A current source is provided which provides a current having a positive temperature coefficient... The emitter of the PNP transistor is connected to one end of the resistor, the base of the PNP transistor is connected to the source of the second NMOS transistor... making the overdrive voltage or the turned-on resistance value of the second NMOS transistor independent of the temperature variation
Implementation Method 2
A current source is provided which provides a current having a positive temperature coefficient... A first end of a resistor is connected to the source of the first NMOS transistor, an emitter of a PNP transistor is connected to a second end of the resistor
Data Source
AI summary
In a driving circuit, a drain of first NMOS transistor receives current with a positive temperature coefficient provided by current source, and a gate of first NMOS transistor and a gate of second NMOS transistor are electrically connected to the drain of first NMOS transistor. A drain and a source of second NMOS transistor respectively receive an input voltage and generate an output voltage for driving a load. Two ends of resistor are respectively electrically connected to a source of first NMOS transistor and an emitter of PNP bipolar junction transistor. A base of PNP bipolar junction transistor is electrically connected to a source of second NMOS transistor, and a collector of PNP bipolar junction transistor is electrically connected to a low voltage. By selecting the resistance value of the resistor, an overdrive voltage or a turned-on resistance value of second NMOS transistor is independent of a temperature variation.