Weak-Inversion MOS Thermal Sensor Circuit for Cross-Node Accuracy
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Solution Overview
Problem
Existing temperature sensing circuit modules experience significant linearity degradation when extended across different technology nodes, particularly in bulk semiconductor and partially depleted semiconductor on insulator (SOI) substrates, affecting their accuracy and reliability in temperature sensing.
Innovation Solution
A temperature sensor circuit design utilizing a first MOS transistor operating in weak inversion mode with a negative temperature coefficient drain-source resistance, coupled with a second MOS transistor operating in strong inversion mode to impose a drain-source current, ensuring a positive temperature coefficient output voltage, while maintaining low power consumption and a compact structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a temperature sensing circuit is implemented using conventional MOS transistor configurations in bulk or partially depleted SOI substrates, then the circuit can be fabricated across different technology nodes, but significant linearity degradation occurs affecting temperature sensing accuracy
Solution Approach 1:
The patent changes the operating parameters of the MOS transistors by biasing them in weak inversion mode with specific gate-source voltages below threshold, and by controlling the body terminal voltages to achieve proper depletion conditions. This parameter adjustment enables linear temperature sensing characteristics across bulk, partially depleted SOI, and fully depleted SOI technology nodes without requiring circuit redesign
Solution Approach 2:
The temperature sensing circuit is designed with universal applicability across multiple substrate types (bulk, partially depleted SOI, fully depleted SOI) and technology nodes. The circuit uses standard MOS transistor structures with controlled biasing conditions that work universally regardless of the specific substrate technology, making the solution broadly applicable throughout the semiconductor industry
2Reliability
If the second MOS transistor operates in strong inversion mode to provide sufficient gate leakage current, then the drain-source current of the first transistor can be properly imposed, but power consumption increases
Solution Approach 1:
The second MOS transistor operates in strong inversion mode which generates sufficient gate leakage current to properly impose the drain-source current of the first transistor. While strong inversion typically consumes more power, the circuit accepts this partial excess action because the current imposition function is critical for accurate temperature sensing, and the overall power consumption remains manageable due to the low current requirements of weak inversion mode operation
3Use of energy by moving object
If the first MOS transistor operates in weak inversion mode to reduce power consumption, then energy efficiency improves, but the drain-source current becomes very small requiring precise control
Solution Approach 1:
The body terminal of the first MOS transistor acts as an intermediary control element. By applying specific body bias voltages, the circuit precisely controls the threshold voltage and operating point of the transistor in weak inversion mode. This intermediary control mechanism enables accurate temperature sensing with very small drain-source currents without requiring excessively complex control circuitry
Solution Approach 2:
The circuit employs feedback through the body terminal control where the voltage at the body terminal is adjusted based on the operating conditions to maintain optimal weak inversion operation. This feedback mechanism automatically compensates for variations and maintains precise control over the small drain-source current, simplifying the overall control requirements
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 provides improved linearity and accuracy in temperature sensing across various technology nodes, with enhanced performance in bulk and SOI substrates, and reduced power consumption, making it suitable for electronic devices.
Implementation Method 1
a first MOS transistor configured to operate in weak inversion mode and have a negative temperature coefficient drain-source resistance
Implementation Method 2
a second MOS transistor configured to operate in strong inversion mode and have a gate leakage current which imposes the drain-source current of the first MOS transistor
Data Source
AI summary
An electronic device includes a module that delivers a positive temperature coefficient output voltage at an output terminal. A thermistor includes a first MOS transistor operating in weak inversion mode and having a negative temperature coefficient drain-source resistance and whose source is coupled to the output terminal. A current source coupled to the output terminal imposes the drain-source current of the first transistor.