ADC Reference Error Cancellation for Variable Resistance Sensors
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Solution Overview
Problem
Existing systems face challenges in accurately detecting the resistance of sensors that vary over time, such as photoresistors, pressure sensors, and thermistors, due to errors introduced by gain errors in analog-to-digital conversion, which affect measurements of light intensity, pressure, and temperature.
Innovation Solution
A system and method that utilize a first and second sensed voltage, generated as products of a voltage reference and unknown and known scalars respectively, with an amplifier and analog-to-digital converter (ADC) to remove errors by using a ratio of digital values, incorporating a linearized current digital-to-analog converter (LIDAC) and programmable gain amplifier (PGA) to achieve ultra-low error detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an analog-to-digital converter (ADC) with a voltage reference and amplifier is used to detect sensor resistance, then the measurement range and functionality are improved, but gain errors in the amplifier and voltage reference introduce measurement errors that worsen detection accuracy
Solution Approach 1:
The system measures the actual output voltage of the amplifier (Vout) and uses this feedback information to calculate a correction factor. This correction factor is then applied to compensate for gain errors in subsequent measurements, allowing the system to maintain high accuracy despite amplifier gain variations.
Solution Approach 2:
The system dynamically adjusts the effective gain by calculating a correction factor based on the ratio of expected to actual output voltages. This parameter change compensates for gain errors without requiring physical modification of the amplifier circuitry.
2Adaptability or versatility
If a voltage reference and amplifier are used in the ADC system, then the ability to measure time-varying resistance is improved, but offset errors in the amplifier introduce additional measurement errors
Solution Approach 1:
The system performs an offset calibration by measuring the output voltage when the input is zero (or known reference). This feedback measurement allows calculation of the offset error, which is then stored and subtracted from subsequent measurements to compensate for offset variations.
Solution Approach 2:
The system performs offset calibration and gain calibration as preliminary actions before actual measurements. These preliminary calibrations establish baseline correction values that are applied during normal operation to eliminate offset and gain errors.
3Stability of the object's composition
If temperature compensation is implemented to reduce temperature sensitivity, then measurement stability over temperature is improved, but the system complexity increases
Solution Approach 1:
The system uses its own internal resources (the amplifier and voltage reference already present in the ADC system) to perform self-calibration. By measuring the actual output and calculating correction factors, the system compensates for temperature drift without requiring external calibration equipment or additional complex temperature sensing circuitry.
Solution Approach 2:
The amplifier and voltage reference serve dual purposes: they perform their primary function of signal amplification and reference voltage generation, and simultaneously enable gain and offset calibration to compensate for temperature variations. This multi-functionality reduces the need for separate temperature compensation components.
Data Source
AI summary
A system includes a first sensed voltage generated as a product of the first voltage reference and an unknown scalar, a second sensed voltage generated as a product of the first voltage reference and a known scalar, and an amplifier having gain error that generates a second voltage reference (first voltage reference or scaled version thereof). An ADC uses the second voltage reference to generate first and second digital values, representing the first and second sensed voltages, that contain error caused by the second voltage reference gain error. A processor uses the known scalar and a ratio based on the first and second digital values to remove the error from the first digital value. The first sensed voltage may be generated by pumping a current into a variable resistance sensor (VRS) whose resistance varies with respect to a time-varying stimulus (e.g., temperature) and is proportional to the unknown scalar.