Resistance Measurement Circuit With Adaptive RC Noise Filtering
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Solution Overview
Problem
The existing resistance measurement systems for thermistors in automobiles suffer from reduced accuracy due to electromagnetic interference (EMI) noise from ignition and injection control systems, which is exacerbated by the use of multiple wire harnesses, leading to increased costs and vehicle weight when countermeasures like twisted pair cables are employed.
Innovation Solution
A semiconductor device with a noise detection system that alternates reference voltages in a time division manner, uses an RC filter with a dynamically adjustable time constant based on noise detection, and incorporates a pre-charge function to reduce measurement time and attenuate noise, thereby improving resistance measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a twisted pair cable is used to reduce EMI noise, then noise attenuation is improved, but part cost and vehicle body weight increase
Solution Approach 1:
The patent introduces an RC filter circuit as an intermediary component between the sensor signal source and the measurement system. The capacitor in the RC filter acts as a mediator that absorbs and attenuates EMI noise from ignition and injection control systems, protecting the thermistor measurement signal without requiring physical cable modifications like twisted pair cables.
Solution Approach 2:
The patent dynamically adjusts the time constant of the RC filter based on operating conditions. By changing the capacitance value or resistance value depending on the operational state (e.g., engine speed, load conditions), the system optimizes noise attenuation while maintaining measurement responsiveness, avoiding the need for always-using heavy shielded cables.
2Object-affected harmful factors
If a twisted pair cable is used to reduce EMI noise, then noise attenuation is improved, but part cost increases
Solution Approach 1:
The RC filter circuit serves as a cost-effective intermediary solution. Instead of investing in expensive twisted pair or shielded cables, the patent uses simple resistor-capacitor components that are inexpensive and easy to integrate into the existing measurement circuitry, significantly reducing part costs while achieving comparable noise attenuation.
Solution Approach 2:
The patent employs inexpensive RC filter components that can be easily replaced or adjusted if needed. These low-cost electronic components serve as a disposable or replaceable solution rather than investing in expensive cable assemblies, making the system more cost-effective for mass production in automobiles.
3Object-affected harmful factors
If the RC filter time constant is increased to attenuate noise, then noise attenuation is improved, but sensor resistivity measurement time increases
Solution Approach 1:
The patent makes the RC filter time constant dynamic rather than fixed. The system adjusts the capacitance or resistance values based on operating conditions - using a longer time constant when noise is present and a shorter time constant when rapid measurement is needed, optimizing both noise attenuation and measurement speed adaptively.
Solution Approach 2:
The system periodically adjusts the RC filter parameters based on detected noise levels or operational phases. During high-noise periods (e.g., during ignition events), the filter time constant is increased for better attenuation. During low-noise periods, the time constant is reduced to enable faster measurements, creating a periodic adaptation cycle.
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 semiconductor device effectively reduces sensor resistivity measurement time and attenuates noise, enhancing the accuracy of resistance measurements while minimizing the need for additional noise-reducing measures that increase cost and weight.
Implementation Method 1
an RC filter disposed on the signal line
Data Source
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.