Thermistor Resistance Measurement With Adaptive RC Noise Filtering
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Solution Overview
Problem
The existing resistance measurement systems for thermistors in automobiles suffer from noise interference due to ignition and injection control signals, leading to reduced accuracy and increased costs with traditional noise attenuation methods like twisted pair cables.
Innovation Solution
A semiconductor device with a ΔΣ ADC, noise detector, and switch control circuit that alternates reference voltages and uses RC filters with adjustable time constants to reduce noise and enhance measurement speed, while pre-charging and pre-buffering techniques improve conversion speed and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If twisted pair cable is used to attenuate noise, then noise attenuation is improved, but part cost and vehicle body weight increase
Solution Approach 1:
The patent replaces the mechanical solution (twisted pair cable) with an electronic solution (RC filter circuit with adjustable time constant). The RC filter, composed of resistor and capacitor, provides noise attenuation through electrical filtering rather than mechanical cable configuration, thereby reducing part cost and vehicle body weight while maintaining noise attenuation performance.
2Object-affected harmful factors
If RC filter with large time constant is used to attenuate noise, then noise attenuation is improved, but measurement time increases
Solution Approach 1:
The patent implements a dynamic time constant adjustment mechanism where the RC filter's time constant is adaptively changed based on operating conditions. The control circuit switches between different resistor or capacitor values to optimize the time constant, allowing the system to achieve effective noise attenuation while minimizing measurement time by using smaller time constants when speed is critical and larger time constants when noise attenuation is prioritized.
3Productivity
If measurement speed is increased, then productivity is improved, but noise attenuation capability deteriorates
Solution Approach 1:
The system dynamically adjusts the RC filter time constant based on measurement requirements. During high-speed measurement modes, the control circuit selects smaller time constant values to enable faster settling and quicker measurements. When noise attenuation is prioritized, larger time constant values are selected. This dynamic adjustment allows the system to optimize between measurement speed and noise attenuation depending on operational conditions.
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 effectively attenuates noise and reduces measurement time for thermistor resistance values, improving accuracy and reducing system costs by optimizing noise filtering and conversion processes.
Implementation Method 1
an RC filter having a time constant that is adjustable according to a presence or absence of the noise
Implementation Method 2
converting a detection signal of a resistance value change type sensor into a digital value
Data Source
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AI summary
A semiconductor device includes first and second terminals, a reference resister being coupled between the first and second terminals, third and fourth terminals, a sensor resister being coupled between the third and fourth terminals, a first buffer which supplies a first reference voltage to the first terminal, a second buffer which supplies a second reference voltage to the fourth terminal, a reference voltage generation circuit which supplies one of first and second voltages alternately in a time division manner as the first reference voltage and supplies the other as the second reference voltage, a first analog-to-digital conversion circuit which performs analog-to-digital conversion on a signal line coupled to the third terminal, an RC filter disposed on the signal line, a noise detector which detects noise of the signal line, wherein a time constant of the RC filter is changed based on a result of the noise detector.