Segmented Pull-Up Resistor for Accurate Thermistor Temperature Measurement
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Solution Overview
Problem
Variations in the resistance values of built-in pull-up resistors in temperature-measuring integrated circuits (ICs) due to processing variations and temperature changes lead to inaccurate external temperature readings when using thermistors as temperature sensors.
Innovation Solution
An integrated circuit design that includes a pull-up resistor with selectable resistance segments and a multiplexer to match a target resistance value, coupled with an analog-to-digital converter to digitize voltages and calculate the thermistor's resistance, allowing for accurate temperature mapping using a temperature-resistance relationship.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a built-in pull-up resistor is used in the integrated circuit, then the circuit integration is improved, but the measurement precision deteriorates due to processing variations and temperature-dependent resistance value changes
Solution Approach 1:
The pull-up resistor is divided into multiple discrete segments with different resistance values. A multiplexer selects specific segments to be connected in parallel, creating an adjustable equivalent resistance that can compensate for manufacturing variations and temperature effects, thereby maintaining measurement precision while keeping the circuit integrated.
Solution Approach 2:
The pull-up resistor configuration is made dynamic through the multiplexer, which can switch between different resistor segments based on temperature conditions or calibration requirements. This dynamic adjustment capability allows the system to optimize the pull-up resistance value for accurate temperature measurements across different operating conditions.
2Ease of manufacture
If the pull-up resistor resistance value is fixed, then the manufacturing process is simplified, but the reliability deteriorates due to die-to-die and temperature-dependent variations
Solution Approach 1:
Instead of manufacturing each pull-up resistor with a precisely fixed value, the design segments the resistor into multiple standard-value segments. The multiplexer selects and combines segments to achieve the required equivalent resistance, making the manufacturing process more robust while maintaining reliability through post-fabrication configurability.
Solution Approach 2:
The system changes the resistance parameter dynamically by selecting different combinations of resistor segments. This allows the pull-up resistance to be adjusted to compensate for die-to-die variations and temperature-dependent effects, ensuring reliable measurements without requiring extremely tight manufacturing tolerances.
3Device complexity
If a single pull-up resistor value is used, then the device complexity is reduced, but the adaptability deteriorates due to inability to compensate for resistance variations
Solution Approach 1:
The pull-up resistor is segmented into multiple selectable portions, and the multiplexer enables different segments to be connected in parallel based on required compensation. This provides adaptability to compensate for resistance variations while maintaining relatively simple circuit architecture compared to using entirely separate adjustable resistors.
Solution Approach 2:
The multiplexer serves multiple functions: it selects resistor segments for the pull-up configuration, enables compensation for variations, and can potentially support different measurement modes. This multi-functionality provides adaptability without proportionally increasing device complexity.
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 enables accurate and consistent external temperature measurements by accounting for die-to-die and temperature-dependent variations in the IC's resistance values, providing precise temperature readouts without the need for further corrections.
Implementation Method 1
connecting a pull-up resistor in series to the thermistor in a voltage divider circuit
Implementation Method 2
an analog-to-digital convertor (ADC) configured to digitize a voltage on the external temperature-dependent resistor
Data Source
AI summary
A method includes using a thermistor as a temperature sensor and connecting a pull-up resistor in series to the thermistor in a voltage divider circuit. The pull-up resistor is fabricated in an integrated circuit and includes a series of resistor segments connected to selectable voltage output tabs. The method further includes selecting an output voltage tab for a selected resistance segment having a selected resistance value to match a target resistance value for the pull-up resistor that is smaller than the as-fabricated resistance value of the pull-up resistor, calculating a ratio of a voltage on the thermistor and a voltage on the selected output voltage tab in the voltage divider circuit, and mapping the calculated ratio to a temperature value of the thermistor based on a temperature-resistance relationship of the thermistor in combination with the target resistance value of the pull-up resistor.