CMOS Temperature Sensor Circuit for Low-Voltage Digital Integration

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Solution Overview

Problem

Bipolar-based temperature sensors require larger power supply rails and occupy more area than MOS transistors, making them challenging to integrate into digital circuits, and their low temperature sensitivity necessitates exponential increases in device size, which is unsustainable with semiconductor scaling.

Innovation Solution

A CMOS-based temperature sensor using MOS transistors generates a reference voltage independent of temperature and digital power supply, integrating a CMOS-based reference voltage generator and temperature front-end circuit to achieve higher sensitivity and compact design, utilizing n-type and p-type MOS transistors to enhance temperature sensitivity without exponential area increases.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If bipolar-based temperature sensors are used, then temperature measurement function is achieved, but power supply requirements increase and area occupation increases

Engineering Contradiction:

Improvetemperature measurement functionVSAvoidsensor area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent changes the fundamental parameter of transistor type from bipolar to MOS, enabling the temperature sensor to operate with lower power supply requirements and reduced area while maintaining measurement functionality through voltage-based temperature coefficient exploitation

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the bipolar transistor mechanism with MOS transistor mechanisms, substituting one physical system for another that achieves the same temperature sensing function with improved area and power characteristics

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If bipolar-based temperature sensors are used, then temperature measurement function is achieved, but device size must increase exponentially to improve temperature sensitivity

Engineering Contradiction:

Improvetemperature sensitivityVSAvoiddevice area

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The patent changes the sensitivity mechanism from current-based in bipolar transistors to voltage-based in MOS transistors, exploiting the temperature coefficient of threshold voltage and mobility to achieve temperature sensitivity without exponential area increases

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of increasing device size to improve sensitivity as done with bipolar sensors, the patent inverts the approach by using MOS transistors where sensitivity is achieved through voltage characteristics rather than current, breaking the exponential area-sensitivity relationship

Inventive Principle:

Principle #13The other way round (Inversion)

3Reliability

If bipolar-based temperature sensors are used, then temperature monitoring is achieved, but integration into digital circuits becomes difficult

Engineering Contradiction:

Improvetemperature monitoring functionVSAvoidintegration compatibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent creates a universal temperature sensor design using MOS transistors that can be integrated with digital circuits, making the sensor adaptable to various digital system architectures and power domains

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent replaces bipolar transistor technology with MOS transistor technology, substituting a system that is incompatible with digital circuits with one that is naturally compatible, enabling seamless integration into modern digital systems

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Reliability

If bipolar-based temperature sensors are used, then temperature sensing is achieved, but power consumption increases

Engineering Contradiction:

Improvetemperature sensing functionVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent changes the power consumption characteristic by switching from bipolar to MOS transistors, which operate at lower voltages and consume less power, while maintaining temperature sensing functionality through voltage-based measurements

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12504333B2CMOS-based temperature sensor

Publication Date: 2025.12.23 APPLE INC

AI summary

A compact low voltage CMOS-based temperature sensor can include a reference voltage generator, a temperature front-end circuit, and an analog-to-digital converter (ADC). The reference voltage generator can be configured to generate a reference voltage independent of temperature. The temperature front-end circuit can include first and second transistors configured to generate a temperature signal proportional to temperature. The first MOS transistor can include first and second terminals. The first terminal can be electrically coupled to the reference voltage. The second terminal can be electrically coupled to the second MOS transistor. The second terminal can provide the temperature signal. The ADC can be electrically coupled to the reference voltage and configured to convert the temperature signal to a digital signal.