Variable Resistance Sensor Measurement With Reference Error Cancellation
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Solution Overview
Problem
Existing resistance measurement technologies face challenges in accurately detecting the resistance of variable resistance sensors (VRS) due to variations in time-varying stimuli, such as temperature, pressure, and light, leading to errors in measurement.
Innovation Solution
A detector system comprising a voltage reference, a linearized digital-to-analog converter (LIDAC), a programmable gain amplifier (PGA), and an analog-to-digital converter (ADC), along with a digital processor, which generates a current to pump into the VRS, senses the voltage, and computes the resistance using known transconductance to minimize errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional resistance measurement system is used, then the measurement process is simple, but the measurement precision deteriorates due to voltage reference variation errors
Solution Approach 1:
The system uses feedback by measuring the voltage across a known reference resistor (Rref) that carries the same current as the VRS, and using this measured voltage to calculate and remove the voltage reference variation error from the resistance measurement. The digital processor computes the corrected resistance using the formula: R_VRS = (V_VRS / V_Rref) * Rref, where V_VRS is the measured voltage across the VRS and V_Rref is the measured voltage across the reference resistor.
Solution Approach 2:
A known reference resistor (Rref) is introduced as an intermediary element to enable error cancellation. By measuring the voltage across this reference resistor that experiences the same current and voltage reference variations as the VRS, the system can mathematically eliminate the voltage reference variation error from the final resistance measurement.
2Measurement precision
If voltage reference variation is not compensated, then the device complexity is low, but the measurement precision deteriorates due to error in resistance measurement
Solution Approach 1:
The system continuously monitors the voltage across the reference resistor and uses this feedback information to calculate and eliminate the voltage reference variation error. The digital processor uses the measured voltages to compute the corrected resistance value, effectively compensating for the harmful voltage reference variations in real-time.
Solution Approach 2:
The voltage reference variation, which is normally a harmful error source, is converted into a useful signal by measuring it across the reference resistor. This measured variation is then used mathematically to cancel out the same error from the VRS measurement, transforming the harmful effect into a beneficial correction mechanism.
3Measurement precision
If a linearized DAC with known transconductance is used, then the measurement precision improves, but the device complexity and chip area increase
Solution Approach 1:
The system changes the operational parameters by using a linearized DAC with known transconductance, which provides a predictable and stable current output in response to digital input codes. This parameter change enables more accurate resistance measurements while the compact integration minimizes the chip area impact.
4Measurement precision
If ultra-low error measurement is achieved through error cancellation, then the measurement precision improves, but the device complexity increases due to additional circuit components
Solution Approach 1:
The system merges the reference resistor measurement function with the VRS measurement function into a single integrated detector circuit. Both measurements are performed simultaneously using the same current source and ADC, reducing the need for separate measurement circuits and minimizing overall device complexity despite the enhanced measurement capabilities.
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 system achieves ultra-low error resistance measurement with high accuracy, low temperature sensitivity, and reduced chip area and power consumption, effectively addressing the challenges of varying resistance sensors.
Implementation Method 1
a linearized digital-to-analog converter (LIDAC) having a known transconductance that uses the voltage reference to generate a current for pumping into the VRS to cause the VRS to generate a voltage sensed by the detector
Implementation Method 2
a voltage reference having variation with respect to operating conditions, and a linearized digital-to-analog converter (LIDAC) having a known transconductance that uses the voltage reference to generate a current
Data Source
AI summary
A detector for measuring a resistance of a variable resistance sensor (VRS) that varies with respect to a time-varying stimulus (e.g., temperature) includes a voltage reference having variation with respect to operating conditions and a linearized digital-to-analog converter (LIDAC) having a known transconductance that uses the voltage reference to generate a current for pumping into the VRS to cause the VRS to generate a voltage sensed by the detector. The sensed voltage includes error due to the variation of the voltage reference. The detector also includes a programmable gain amplifier (PGA) that gains up the sensed voltage to generate an output signal, an ADC that converts the output signal to a digital value, and a digital processor that computes the resistance of the VRS using the digital value and the known transconductance. The PGA is non-varying with respect to the time-varying stimulus.