Sub-threshold CMOS Temperature Detector Circuit
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Solution Overview
Problem
Integrated circuits (ICs) face challenges in temperature detection due to varying electrical characteristics with temperature changes, requiring accurate detectors to compensate for deviations from normal operating conditions, while also needing low power consumption and functionality at low supply voltages, which are exacerbated by reduced feature sizes and lower operating voltages.
Innovation Solution
A low supply voltage and low power consumption temperature detector circuit utilizing sub-threshold CMOS technology to generate a Proportional to Absolute Temperature (PTAT) current, which passes through a resistor and a PNP bipolar transistor, producing PTAT and inverse PTAT voltages for comparison by a comparator to generate an alarm signal, allowing operation at voltages below 1V and consuming about 2.5 uA current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional temperature detection circuits are used, then temperature detection accuracy is maintained, but power consumption increases and operation at low supply voltages becomes difficult
Solution Approach 1:
The patent changes the operating parameters of the CMOS transistors by utilizing sub-threshold operation, where the gate-source voltage is below the threshold voltage. This allows the circuit to operate at very low supply voltages (below 1V) and consume minimal power (about 2.5 uA) while maintaining temperature detection functionality through the exponential relationship between sub-threshold current and temperature
Solution Approach 2:
The patent replaces conventional temperature sensing mechanisms with a CMOS-based sub-threshold current generation approach. Instead of using traditional bandgap references or PTAT circuits that require higher voltages, the invention uses the natural sub-threshold characteristics of MOSFETs to generate temperature-proportional currents, eliminating the need for complex reference voltage circuits
2Length of moving object
If feature sizes of ICs are reduced to improve integration, then operating voltage decreases, but temperature sensor design becomes more challenging due to inconsistent semiconductor device characteristics
Solution Approach 1:
The patent exploits the sub-threshold operation regime where transistor characteristics become less sensitive to process variations and dimensional tolerances. By operating in this regime, the circuit maintains consistent temperature detection performance across different feature sizes and manufacturing tolerances, making it suitable for scaled CMOS technologies
Solution Approach 2:
The circuit uses the inherent sub-threshold characteristics of standard CMOS transistors without requiring special devices or structures. The transistors naturally exhibit the required exponential current-voltage relationship in sub-threshold mode, eliminating the need for specialized temperature-sensing transistor designs or additional manufacturing steps
3Measurement precision
If constant reference voltage is used for temperature detection, then detection accuracy is improved, but power consumption increases
Solution Approach 1:
The patent extracts and eliminates the constant reference voltage component from the temperature detection circuit. Instead of using a separate voltage reference generator that consumes power, the invention generates the reference signal directly from the sub-threshold current, which is inherently temperature-proportional and requires no additional power-consuming reference circuits
Solution Approach 2:
The sub-threshold current serves multiple functions simultaneously: it acts as the temperature sensing signal, the reference signal for comparison, and the operating current for the logic circuits. This multi-functionality eliminates the need for separate reference voltage generators and reduces overall power consumption while maintaining detection accuracy
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 temperature detection within predefined limits without a constant reference voltage, allowing for power-efficient operation and adaptive frequency adjustments in ICs, ensuring reliable performance across temperature variations while preserving battery power in portable devices.
Implementation Method 1
utilizing sub-threshold CMOS technology to generate a Proportional to Absolute Temperature (PTAT) current
Implementation Method 2
The PTAT current passes through a resistor and a PNP bipolar transistor, generating a PTAT voltage and an inverse PTAT voltage
Data Source
AI summary
A CMOS temperature detection circuit includes a start-up circuit for generating a start-up voltage (VN), and a proportional to absolute temperature (PTAT) current generator coupled to the start-up circuit for generating a PTAT current. The start-up voltage turns on the PTAT current generator, and the PTAT current generator uses the sub-threshold characteristics of CMOS to generate the PTAT current. A PTAT voltage generator coupled to the PTAT current generator receives the PTAT current and generates a PTAT voltage and an inverse PTAT voltage (VBE). A comparator circuit coupled to the voltage generator compares the inverse PTAT voltage to first and second alarm limits, which are defined using the generated PTAT voltage, and generates an alarm signal based on the comparison results.