Resistive Sensor Interface Using One ADC for Accurate Ratio Measurement
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Solution Overview
Problem
Existing technologies face challenges in efficiently measuring unknown resistances, particularly in automotive sensor electronics, where the variation of electrical resistance is proportional to the physical quantity being measured, requiring accurate calculation of unknown resistances using a known reference resistance.
Innovation Solution
A device comprising a reference resistance and an unknown resistance connected in series, with a single analog-to-digital converter that efficiently measures and processes voltages across both resistances, utilizing changeover-switch modules and multiplexers to determine the digital representation of the unknown resistance, optimizing analog-to-digital operations for accuracy and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two separate analog-to-digital converters are used to measure voltages across reference and unknown resistances, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent combines two separate analog-to-digital conversion functions into a single ADC by time-multiplexing the input signals. The switch alternately connects the ADC to the reference voltage divider circuit and the unknown resistance measurement circuit, allowing one converter to perform the work of two while maintaining measurement accuracy through sequential sampling.
Solution Approach 2:
The measurement system uses periodic switching to alternate between measuring the reference voltage and the unknown resistance voltage. The switch operates in periodic cycles, connecting to different measurement circuits at different time intervals, enabling a single ADC to sequentially perform multiple measurement tasks with high precision.
2Reliability
If multiple analog-to-digital operations are performed sequentially, then measurement completeness is improved, but measurement time increases
Solution Approach 1:
The system implements periodic switching between different measurement channels, allowing the ADC to rapidly alternate between measuring reference voltages and unknown resistance voltages. This time-division multiplexing approach ensures both measurements are completed within each measurement cycle, maintaining completeness while minimizing total measurement time.
Solution Approach 2:
The measurement process maintains continuous operation by seamlessly switching between different measurement tasks without idle periods. The ADC continuously converts incoming signals from either the reference circuit or unknown resistance circuit, ensuring that useful measurement actions are performed continuously throughout the measurement 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 solution provides efficient and precise measurement of unknown resistances, requiring fewer analog-to-digital operations and achieving greater accuracy by effectively handling different conditions between the unknown and reference resistances, ensuring reliable sensor data in automotive applications.
Implementation Method 1
The two resistances RREF and RX are set in series and connected between the supply voltage VSUP and ground gnd. The current IX that flows in the unknown resistance Rx is VSUP/(RREF+RX). Consequently, the value of the unknown resistance Rx can be calculated, as a function of the quantities identified in the circuit
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A device for measuring an unknown resistance (RX), comprising a reference resistance (RREF) in series with the unknown resistance (RX). The device is prearranged for measuring a first voltage (V1) and a second voltage (V2), across the reference resistance (RREF) and of the unknown resistance (RX), respectively. The device comprises changeover-switch modules (muxA, muxB), which receive at input the first voltage (V1) and the second voltage (V2) and supply values (D1, D2) representing the first voltage (V1) and the second voltage (V2), and a single analog-to-digital converter (ADC), which supplies at output the digital representation (DX) of the value of the unknown resistance (RX) as ratio between the values (D1, D2) at input to the converter (ADC). The analog-to-digital converter (ADC) contains two negative feedback loops (D2, D1), which function in an alternative way according to the outputs of the changeover-switch modules (muxA, muxB). The negative feedback loops (D2, D1) are first-order continuous-time sigma-delta converters. In particular, one of the two sigma-delta converters has a constant digital output at the level "1".