Strain-Insensitive Temperature Sensor Using Switched-Capacitor Reference
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Solution Overview
Problem
Integrated circuit temperature sensors face accuracy issues due to sensitivity to mechanical strain and aging, which can cause unpredictable shifts in temperature measurements, making it challenging to achieve precise temperature sensing.
Innovation Solution
A temperature sensing apparatus and method utilizing a thermistor with variable resistance and a reference resistor with opposite temperature dependence, coupled with a switched-capacitor circuit, generate a strain-invariant signal proportional to a reference voltage, effectively compensating for strain and aging effects by maintaining a node at a predetermined voltage level using an operational amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermistor is used for temperature sensing, then temperature sensitivity is improved, but strain sensitivity increases causing measurement inaccuracy
Solution Approach 1:
The patent introduces a reference resistor as an intermediary element that is insensitive to strain but responds to temperature. By comparing the thermistor's resistance (which is affected by both temperature and strain) with the reference resistor's resistance (affected only by temperature), the strain component can be mathematically eliminated, yielding an accurate temperature measurement independent of strain effects
Solution Approach 2:
The patent changes the measurement parameter from absolute resistance values to a ratio of resistance values (thermistor resistance divided by reference resistor resistance). This parameter transformation eliminates the strain-dependent component while preserving the temperature-dependent component, as the strain effect appears as a common factor that cancels out in the ratio
2Measurement precision
If strain compensation mechanisms are added to the integrated circuit, then temperature measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
Instead of using complex strain sensors and active compensation circuits, the patent employs a simple passive reference resistor as an intermediary that naturally provides strain-insensitive behavior. This approach achieves compensation through the inherent properties of the reference component rather than through active sensing and correction mechanisms
Solution Approach 2:
The patent replaces expensive and complex strain compensation mechanisms with a simple, inexpensive reference resistor that can be easily fabricated using standard integrated circuit processes. The reference resistor serves as a disposable, low-cost element that eliminates the need for sophisticated strain sensing and compensation circuitry
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 accuracy and reduced sensitivity to strain and aging, resulting in a more reliable and precise temperature measurement system, even in the presence of mechanical stress and environmental changes.
Implementation Method 1
a thermistor having a variable resistance with a first dependence on absolute temperature
Implementation Method 2
a reference resistor having a reference resistance with a second dependence on absolute temperature
Implementation Method 3
The apparatus may include a feedback circuit configured to maintain the node at a predetermined voltage level. The feedback circuit may include an operational amplifier configured to receive the signal from the node at a virtual ground of the operational amplifier
Data Source
AI summary
An apparatus includes a thermistor having a variable resistance with a first dependence on absolute temperature. The apparatus includes a reference resistor having a resistance with a second dependence on absolute temperature, the second dependence being less than or having opposite polarity to the first dependence. The reference resistor includes a switched-capacitor circuit. The apparatus includes a node coupled between the thermistor and the reference resistor. The node is configured to provide a signal indicative of absolute temperature based on the variable resistance and the reference resistance. The signal may be strain-invariant, proportional to a reference voltage, and indicative of a ratio of the variable resistance to the reference resistance. The apparatus may include a feedback circuit configured to maintain the node at a predetermined voltage level.