On-Chip Temperature Sensor Circuitry with Offset Cancellation
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Solution Overview
Problem
Temperature sensors in semiconductor devices often exhibit poor measurement accuracy, leading to delayed reduction in power consumption and increased risk of overheating, which can cause destructive failure.
Innovation Solution
The implementation of temperature sensing circuitry on a semiconductor integrated circuit that uses offset cancellation techniques to generate a current signal proportional to temperature, coupled with an analog-to-digital converter (ADC) and bandgap reference generator, to provide a more accurate digital representation of temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional temperature sensors are used in semiconductor devices, then the device complexity is reduced, but the measurement precision deteriorates
Solution Approach 1:
The temperature sensing function is divided into multiple independent components: a PTAT current generator for temperature-proportional signal generation, a CTAT current generator for reference signal generation, an ADC for analog-to-digital conversion, and a digital processor for temperature calculation. This segmentation allows each component to be optimized independently while achieving high measurement precision through their coordinated operation.
Solution Approach 2:
The patent introduces intermediate signal processing stages between the temperature sensing elements and the final digital output. The PTAT and CTAT current generators create intermediate current signals that are converted to digital values through the ADC, then processed by the digital processor to calculate the final temperature. These intermediary stages enable precise temperature measurement by transforming physical temperature signals into processed digital data through multiple conversion and calculation steps.
2Reliability
If temperature sensors with basic functionality are implemented, then the device complexity is reduced, but the reliability deteriorates
Solution Approach 1:
The patent implements feedback mechanisms through the CTAT current generator that generates a reference current proportional to the inverse of absolute temperature. This reference current is fed back to the ADC and digital processor to compensate for temperature drift in the PTAT generator and other circuit components. The feedback loop continuously adjusts the measurement based on temperature conditions, ensuring reliable temperature monitoring even as circuit characteristics change with temperature.
Solution Approach 2:
The patent utilizes parameter changes in semiconductor physics to achieve temperature compensation. The PTAT generator exploits the property that the base-emitter voltage of bipolar transistors changes linearly with temperature, while the CTAT generator utilizes the inverse temperature dependence of carrier concentration. By changing the operating parameters of these generators based on temperature conditions, the system maintains measurement reliability across a wide temperature range despite variations in process conditions and aging.
3Loss of time
If temperature sensors with poor accuracy are used, then the device complexity is reduced, but the loss of time increases
Solution Approach 1:
The patent performs preliminary temperature measurement and processing actions continuously in the background, even before temperature thresholds are exceeded. The PTAT and CTAT current generators operate continuously to provide real-time temperature data to the ADC and digital processor. This preliminary action ensures that when temperature does exceed thresholds, the system already has current temperature information and can respond immediately without delay, as the sensing and processing circuits are always in an active state ready for rapid response.
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 enhances temperature measurement accuracy, enabling timely power reduction and preventing overheating in semiconductor devices.
Implementation Method 1
generates a current signal that is proportional to the sensed temperature using offset cancellation techniques
Implementation Method 2
Similar offset cancellation techniques are employed in generation of the bandgap reference signal provided to the ADC
Implementation Method 3
The current signal is provided to an input of an analog-to-digital converter (ADC). At the completion of a conversion, the ADC provides a digital value more accurately representative of the sensed temperature
Data Source
AI summary
An on-chip temperature sensor generates a proportional to absolute temperature current and sloped bandgap reference current with transistor offset cancelled using chopping circuitry and dynamic element matching circuitry with resistor-based current mirrors. A digital successive approximation register (SAR) code provided to a digital to analog converter (DAC) is adjusted until current output by the DAC matches the PTAT current.