Sub-threshold CMOS Temperature Sensor for Low Power Chip Monitoring
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Solution Overview
Problem
Conventional bipolar-based temperature sensors on chips are power-intensive, occupy large areas, and require separate analog power supply rails, limiting their placement and accuracy in monitoring hot spots within digital logic circuits like CPUs.
Innovation Solution
A temperature sensor design utilizing two N-type field-effect transistors operating in the sub-threshold region, with a bias circuit that generates a current proportional to temperature, and an analog-to-digital converter to produce a digital reading, allowing for smaller size, lower power consumption, and operation using digital logic supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bipolar-based temperature sensors are used on chips, then temperature monitoring function is achieved, but power consumption increases and area occupied increases
Solution Approach 1:
The patent changes the operating parameters of the transistors by biasing them in the sub-threshold region rather than the conventional active region. This parameter change enables the temperature sensor to achieve accurate temperature monitoring while consuming significantly less power, as sub-threshold operation reduces dynamic power consumption while maintaining sufficient signal generation for temperature sensing.
Solution Approach 2:
The patent uses different transistor types (first N-type and second P-type transistors) with complementary characteristics in the differential pair configuration. This local quality differentiation allows the circuit to generate a temperature-dependent output signal while maintaining low power consumption and small area footprint suitable for integration on digital chips.
2Reliability
If bipolar-based temperature sensors are used on chips, then temperature monitoring function is achieved, but area occupied increases
Solution Approach 1:
By operating transistors in the sub-threshold region and using a differential pair configuration, the patent achieves accurate temperature sensing with a compact circuit design. The use of complementary N-type and P-type transistors in a differential configuration provides temperature-dependent output with minimal area requirement, suitable for integration alongside digital logic circuits on the same chip.
3Reliability
If bipolar-based temperature sensors are used, then temperature monitoring is achieved, but separate analog power supply rails are required
Solution Approach 1:
The patent designs the temperature sensor using standard CMOS transistors that can be powered by the same digital logic supply voltages already present on the chip. This universal power supply approach eliminates the need for separate analog power rails, simplifying the power supply configuration and enabling easier integration with existing digital circuits while maintaining accurate temperature sensing capability.
4Measurement precision
If multiple temperature sensors are integrated on chip, then temperature monitoring coverage is improved, but power consumption and area increase
Solution Approach 1:
By operating multiple temperature sensors in sub-threshold mode with complementary transistor pairs, each sensor consumes minimal power. This enables the integration of multiple sensors across different locations on the chip to achieve comprehensive temperature monitoring coverage while keeping the total power consumption of all sensors combined well below that of conventional bipolar-based sensors.
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
Enables accurate, compact, and power-efficient temperature monitoring within digital logic circuits, allowing for increased density of temperature sensors on chips and precise temperature management to prevent overheating.
Implementation Method 1
a bias circuit configured to bias the gates of the first and second transistors such that the first and second transistors operate in a sub-threshold region, and to generate a current proportional to a difference between a gate-to-source voltage of the first transistor and a gate-to-source voltage of the second transistor
Implementation Method 2
an analog-to-digital converter (ADC) configured to convert the current into a digital temperature reading
Data Source
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AI summary
Systems and methods for sensing temperature on a chip are described herein. In one embodiment, a temperature sensor comprises a first transistor having a gate, a second transistor having a gate coupled to the gate of the first transistor, and a bias circuit configured to bias the gates of the first and second transistors such that the first and second transistors operate in a sub-threshold region, and to generate a current proportional to a difference between a gate-to-source voltage of the first transistor and a gate-to-source voltage of the second transistor. The temperature sensor also comprises an analog-to-digital converter (ADC) configured to convert the current into a digital temperature reading.