Resistive Sensor Interface Using One ADC for Precise Ratio Measurement
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Solution Overview
Problem
Existing technologies face challenges in efficiently measuring unknown resistances using a reference resistance of known value, particularly in sensor electronic interfaces for automotive applications, where accurate and precise calculations of resistance ratios are necessary for physical quantity measurements like liquid levels and temperatures.
Innovation Solution
A device comprising a reference resistance in series with the unknown resistance, utilizing changeover-switch modules and a single analog-to-digital converter with negative feedback loops, specifically first-order continuous-time sigma-delta converters, to calculate the digital representation of the unknown resistance as a ratio of measured voltages across the resistances, optimizing the architecture for efficient and accurate measurements.
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 and cost increase
Solution Approach 1:
The patent combines two separate analog-to-digital conversion functions into a single ADC by implementing a dual-slope integrating converter that sequentially integrates two input voltages (V1 across reference resistance and V2 across unknown resistance). This merging approach maintains measurement accuracy by comparing the unknown resistance voltage against the reference resistance voltage through integrated areas, while reducing device complexity and cost by eliminating the need for two separate ADCs.
Solution Approach 2:
The single ADC is designed to perform multiple functions: it can measure both the reference voltage and the unknown voltage, perform integration operations, and execute the comparison calculation all within one converter unit. The integrating converter architecture provides universal functionality that handles both measurement tasks and the subsequent ratio calculation, replacing what would traditionally require separate dedicated circuits.
2Speed
If multiple analog-to-digital converters are used, then measurement speed is improved, but productivity and efficiency decrease due to increased operational overhead
Solution Approach 1:
The integrating ADC operates using periodic action by sequentially integrating the reference voltage during one time period and then integrating the unknown voltage during another time period. This time-sequential approach allows a single converter to achieve measurement speeds comparable to multiple parallel converters, while the continuous periodic operation maintains high productivity without the overhead of coordinating multiple independent conversion processes.
Solution Approach 2:
The integrating converter maintains continuous useful action by immediately transitioning from integrating the reference voltage to integrating the unknown voltage without idle periods. This continuous operation ensures that the single ADC achieves maximum measurement throughput, eliminating wasted time that would occur with startup/stop sequences or calibration periods between measurements.
3Device complexity
If a single analog-to-digital converter is used, then device complexity is reduced, but measurement precision may deteriorate
Solution Approach 1:
The integrating ADC employs feedback mechanisms where the integration results of the reference voltage are used as a reference for comparing against the unknown voltage integration results. This feedback-based comparison approach ensures that measurement precision is maintained by continuously referencing the known standard against the unknown quantity, compensating for any drift or errors that might occur in a single-converter system.
Solution Approach 2:
The patent uses a composite measurement approach by combining multiple measurement functions (voltage integration, time measurement, ratio calculation) into a single converter system. This composite architecture integrates different functional elements within one ADC unit, maintaining the precision benefits of multiple converters while achieving the simplicity of a single device through functional integration.
Data Source
AI summary
A device to read a variable resistor has an analog to digital converter (ADC), a first switch and a second switch. The ADC has a first ADC input, a second ADC input and an ADC output. The first switch selectively couples a first voltage indicative of a voltage across a first resistance to the first ADC input. The second switch selectively couples a second voltage indicative of a voltage across a second resistance to the second ADC input. The ADC outputs a signal indicative of a value of the second resistance.