ADC Reference Circuit for Calibration-Free Thermistor Measurement
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Solution Overview
Problem
Existing temperature measurement methods for electronic circuits, such as those using thermistors, are prone to errors due to variations in external voltage supply and internal voltage reference accuracy, requiring calibration that increases circuit complexity and cannot correct errors occurring after power-up.
Innovation Solution
An analog-to-digital converter (ADC) architecture that includes a reference generator biased from the same voltage supply as the temperature measurement element, allowing for ratiometric measurements that eliminate the need for calibration by canceling out supply voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If calibration is performed to reduce measurement errors, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The measurement system automatically compensates for supply voltage variations through self-calibration using the ADC's internal reference voltage, eliminating the need for external calibration procedures. The system serves itself by using its own reference voltage to correct measurement errors, thereby improving measurement precision without increasing device complexity.
Solution Approach 2:
The invention changes the reference voltage parameter from an external fixed reference to an internal reference that is inherently tied to the ADC's supply voltage. This parameter change enables automatic compensation for supply variations, achieving high measurement precision without requiring additional calibration circuitry or procedures.
2Measurement precision
If calibration is performed at power-up to correct errors, then measurement precision is improved, but ease of operation deteriorates
Solution Approach 1:
The system performs automatic self-calibration using its internal reference voltage without requiring user intervention. The calibration process is transparent to the user, who simply connects the thermistor and receives accurate temperature readings without needing to perform any calibration steps, thereby maintaining ease of operation while achieving high measurement precision.
Solution Approach 2:
The system incorporates built-in reference voltage generation that is automatically established when power is applied, preparing the measurement system in advance without requiring user action. The reference voltage is ready immediately upon power-up, enabling instant accurate measurements without manual calibration preparation.
3Measurement precision
If a fixed reference voltage is used for comparison, then measurement precision is improved, but adaptability deteriorates
Solution Approach 1:
The reference voltage is made dynamic by deriving it from the ADC's supply voltage through an internal voltage divider network. As the supply voltage changes with temperature, the reference voltage automatically adjusts to maintain an appropriate ratio for accurate thermistor measurements across the entire operating temperature range, thereby achieving both measurement precision and adaptability.
Solution Approach 2:
The invention changes the reference voltage from a fixed value to a variable parameter that automatically tracks supply voltage changes. This parameter change enables the system to adapt to different operating conditions and temperature ranges while maintaining accurate measurements through proportional scaling of the reference voltage.
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 approach provides precise temperature measurements without calibration, reducing errors caused by supply voltage and reference accuracy variations, ensuring accurate temperature monitoring in harsh operating conditions.
Implementation Method 1
The reference generator is operative to generate the reference voltage as a function of the external voltage supply
Implementation Method 2
A thermistor is a well-known type of device having a resistance that varies significantly with temperature
Data Source
AI summary
A measurement circuit is provided for measuring the resistance of a variable resistance element biased with an external voltage supply. The measurement circuit includes an analog-to-digital converter (ADC) and a reference generator connected with the ADC. The ADC is operative to receive a reference voltage and a first voltage developed across the variable resistance element, and to generate a digital output signal indicative of a relationship between the first voltage and the reference voltage. The reference generator is operative to generate the reference voltage as a function of the external voltage supply.