A Novel Dual-Slope Resistance-to-Digital Converter
08 Jan 2010-IEEE Transactions on Instrumentation and Measurement (IEEE)-Vol. 59, Iss: 5, pp 1013-1018
TL;DR: A dual-slope resistance-to-digital (DSRDC) converter that accepts the resistance of a single-element resistive-type sensor as input and provides a direct digital output proportional to the parameter being sensed by the resistive -type sensor is presented.
Abstract: A dual-slope resistance-to-digital (DSRDC) converter that accepts the resistance of a single-element resistive-type sensor as input and provides a direct digital output proportional to the parameter being sensed by the resistive-type sensor is presented in this paper. A high level of linearity and accuracy is achieved since the output of the DSRDC is dictated only by the magnitudes of a pair of dc reference voltages and the transformation constant of the sensor. Sensitivity analysis shows that the effect of circuit parameter variations on the output is minimal. Simulation studies and test results obtained on a prototype establish the efficacy of the proposed scheme.
Citations
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TL;DR: A direct sensor-to-microcontroller interface scheme that compensates the effect due not only to resistances of lead wires but also the effect of microcontroller port pin’s internal resistance and any offset present in those pins is presented in this paper.
Abstract: Direct resistive sensor interface to a microcontroller has several advantages but has one prominent disadvantage, namely, the measurement is affected by the resistances of: 1) wires that connect the sensor to the port pins and 2) the internal resistances of the port pins of the microcontroller. A direct sensor-to-microcontroller interface scheme that compensates the effect due not only to resistances of lead wires but also the effect of microcontroller port pin’s internal resistance and any offset present in those pins is presented in this paper. Since the resistances of lead wires are compensated, automatic temperature compensation (temperature effect of lead wires) is also obtained. Simulation study and results obtained from a prototype built and tested establish the efficacy of the proposed method. A maximum error of 0.06% was observed from the prototype developed, when it was tested under room temperature, after interfacing it with the sensor Pt100, with a lead wire resistance $R_{\mathrm {LD}} = 21~\Omega $ . The error increased to a maximum of 0.08%, when the $R_{\mathrm {LD}}$ varied from 0 to $100~\Omega $ . When the same prototype was tested under elevated room temperature of 30 °C to 100 °C, the maximum error observed was 0.18%.
58 citations
Cites background from "A Novel Dual-Slope Resistance-to-Di..."
...a digital output dispensing with analog signal conditioning circuits [14], [15]....
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TL;DR: A novel readout circuit for interfacing single element resistive sensors is presented, based on a new relaxation oscillator (RO), which provides a digital output proportional to the resistance of the sensor.
Abstract: A novel readout circuit for interfacing single element resistive sensors is presented in this paper. The proposed scheme is based on a new relaxation oscillator (RO). The RO, along with a timer counter provides a digital output proportional to the resistance of the sensor. The output characteristic of most of the existing readout circuits for resistive sensors suffers from gain, offset, and nonlinearity errors. The sources of errors include various nonideal circuit parameters and their drift. The output of the proposed readout circuit has a special feature that it is not a function of the circuit parameters such as: 1) offset voltages of the opamps and comparators; 2) bias currents of the opamps and comparators; 3) gain of various units employed; 4) ON-resistance of the switches; 5) value or mismatch in the magnitudes of the reference voltages employed; 6) delay of the switches and comparator; 7) leakage current of the switch; and 8) slew rate of the opamp. Such a scheme will be useful for high accuracy measurements, even when the parameters 1)–8) may vary or drift, due to variation in the measurement environment. A prototype of the proposed readout scheme has been developed in the laboratory and the performance has been evaluated under various conditions. The output was found to be linear with a worst-case nonlinearity of 0.05%. Test results from a prototype developed show that the proposed scheme possesses all the features, described above, as expected.
33 citations
Cites background from "A Novel Dual-Slope Resistance-to-Di..."
...As can be seen in most of the existing resistance measurement techniques [9], [12], [13], the value of the ON resistance RON of the switch S1 is a noticeable source of error, for low resistance measurements (Rx < 1 k )....
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...In [12], each measurement is repeated for 25 times and an average is taken to improve the precision....
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...and timer counter [2]–[4], while the others rely on a resistance to pulsewidth conversion [5], resistance-to-time conversion [6]–[8], sigma–delta [9], resistance-to-frequency conversion [10], [11], charge-balancing type [12], [13],...
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TL;DR: In this article, an improved direct digital converter (IDDC) suitable for bridge-connected resistive sensors is presented, where the input stage of a dual-slope analog-to-digital converter is altered to accommodate a resistive sensor bridge, as its integral part and the logic of conversion incorporate automatic compensation for offset, offset drift and gain errors.
Abstract: An improved direct digital converter (IDDC) suitable for bridge-connected resistive sensors is presented in this paper. The input stage of a dual-slope analog-to-digital converter is altered to accommodate a resistive sensor bridge, as its integral part and the logic of conversion incorporate automatic compensation for offset, offset drift, and gain errors. Through a detailed error analysis of the DDC presented earlier, the effects of the non-ideal characteristics of practical components on the performance of the DDC are quantified. From the analysis, it is determined that mismatch between the bridge elements and the input offset of op-amps significantly affect the output. While the earlier version of the DDC requires offline correction for offset and gain errors, the proposed IDDC provides in situ correction for these and hence can also compensate drifts. Simulation studies and experimental results demonstrate the practicality of the proffered scheme and indicate that the worst case error of ±0.2% due to offset in op-amps and mismatch in nominal resistances of sensing elements reduces to ±0.05% with the use of the proposed compensation technique.
25 citations
Cites background from "A Novel Dual-Slope Resistance-to-Di..."
...Direct Digital Conversion (DDC) schemes suitable for single element and push-pull type resistive sensors have been reported earlier [16], [17]....
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TL;DR: A readout circuit for a resistive CO2 sensor, which operates by measuring the CO2-dependent thermal conductivity of air, using dynamically-swapped transducer pairs to cancel their baseline-resistance, so as to relax the required dynamic range of the ADC.
Abstract: This paper reports a readout circuit for a resistive CO2 sensor, which operates by measuring the CO2-dependent thermal conductivity of air. A suspended hot-wire transducer, which acts both as a resistive heater and temperature sensor, exhibits a CO2-dependent heat loss to the surrounding air, allowing CO2 concentration to be derived from its temperature rise and power dissipation. The circuit employs a dual-mode incremental delta-sigma ADC to digitize these parameters relative to those of an identical, but isolated, reference transducer. This ratiometric approach results in a measurement that does not require precision voltage or power references. The readout circuit uses dynamically-swapped transducer pairs to cancel their baseline-resistance, so as to relax the required dynamic range of the ADC. In addition, dynamic element matching (DEM) is used to bias the transducer pairs at an accurate current ratio, making the measurement insensitive to the precise value of the bias current. The readout circuit has been implemented in a standard 0.16 $\mu \text {m}$ CMOS technology. With commercial resistive micro-heaters, a CO2 sensing resolution of about 200 ppm ( $1\sigma $ ) was achieved in a measurement time of 30 s. Similar results were obtained with CMOS-compatible tungsten-wire transducers, paving the way for fully-integrated CO2 sensors for air-quality monitoring.
21 citations
Cites background from "A Novel Dual-Slope Resistance-to-Di..."
...They either rely on a ‘dummy’ passive element but assume negligible mismatch errors introduced by manufacturing tolerances [22], [23], or require a dedicated calibration phase involving extra analog-to-digital...
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...Many approaches have been reported to cancel baseline resistance [22]–[25]....
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TL;DR: An improved digital interface circuit for resistive sensors that offers use of single-reference voltage in its architecture, facility to tune/preset the sensor-excitation current, and minimal dependence on many circuit non-ideal parameters is proposed.
Abstract: An improved digital interface circuit for resistive sensors is proposed in this paper. The circuit offers many positive features, such as (1) use of single-reference voltage in its architecture, (2) facility to tune/preset the sensor-excitation current, even for different values of resistive sensors, (3) minimal dependence on many circuit non-ideal parameters. The working of the circuit is mathematically described in this paper, followed by its extensive error evaluation. Detailed simulation and experimental studies are performed to verify the feasibility of the interface for three different types of sensors. These studies show that the circuit can efficiently be used in temperature-monitors, magnetometers, and displacement-sensing. The maximum experimental nonlinearity observed from all of these sensor configurations does not exceed 0.06 %. Then, the extensive studies are carried out by simulation as well as experimentation to show the effect of environmental temperature changes on the proposed circuit. Finally, the proposed circuit is compared with some of the recent resistive digital interfaces.
16 citations
Cites background from "A Novel Dual-Slope Resistance-to-Di..."
...The conversion time is 10 ms, lower than reported values in [15], [23], and [25]....
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...Some of the other schemes ([23]–[25], [27]) are dependent on RN ....
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...This DCR architecture is a modified and improved version of the dual-slope-based works presented in [23]–[25] and [27]....
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...This feature is absent in many of the previous works ([23], [24])....
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...Note that the other schemes ([23], [24], [27]) need bipolar and matched dual reference voltages....
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References
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Book•
01 Jan 1966TL;DR: This paper aims to provide a history of ecoulement and mesures used in this discipline over a 25-year period and aims to establish a chronology of events leading up to and including the invention of EMT.
Abstract: Part 1 General Concepts 1 Types of Applications of Measurement Instrumentation 2 Generalized Configurations and Functional Descriptions of Measuring Instruments 3 Generalized Performance Characteristics of Instruments Part 2 Measuring Devices 4 Motion and Dimensional Measurement 5 Force, Torque, and Shaft Power Measurement 6 Pressure and Sound Measurement 7 Flow Measurement 8 Temperature and Heat-Flux Measurement 9 Miscellaneous Measurements Part 3 Manipulation, Transmission, and Recording of Data 10 Manipulating, Computing, and Compensating Devices 11 Data Transmission and Instrument Connectivity 12 Voltage-Indicating and -Recording Devices 13 Data-Acquisition Systems for Personal Computers 14 Measurement Systems Applied to Micro- and Nanotechnology
913 citations
"A Novel Dual-Slope Resistance-to-Di..." refers methods in this paper
...To obtain a measurable voltage or current output from a passive sensor, such as the resistive type, an analog-signal-conditioning circuit is required [ 1 ]....
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TL;DR: Novel CMOS switched-capacitor circuits for high-accuracy, on-chip capacitive-ratio testing and sensor readout using sigma-delta and correlated-double-sampling (CDS) techniques are presented.
Abstract: This paper presents novel CMOS switched-capacitor circuits for high-accuracy, on-chip capacitive-ratio testing and sensor readout. Using sigma-delta and correlated-double-sampling (CDS) techniques, these circuits provide accurate digitized capacitive-ratio readout. Both single-ended and fully differential circuits are presented. Simulation results show that the resolution can be as fine as 100 aF for 10 pF capacitors. Single-ended circuit and fully-differential circuits were implemented and tested. The measured standard deviation was below 20 aF when 10 pF capacitors were tested.
58 citations
"A Novel Dual-Slope Resistance-to-Di..." refers background in this paper
...Some of the earlier attempts in this direction resulted in digital converters that are suitable for capacitance-type sensors [2]–[4]....
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TL;DR: In this paper, an improved dual-slope analog-to-digital converter for measurements made with a pair of resistive or capacitive differential transducers is described, which can be contrasted with the conventional method in which the transducers are placed in a bridge, the bridge output is amplified, and the conversion is made.
Abstract: An improved dual-slope analog-to-digital converter for measurements made with a pair of resistive or capacitive differential transducers is described. The converter can be contrasted with the conventional method in which the transducers are placed in a bridge, the bridge output is amplified, and the conversion is made. In the new converter the transducers are part of the integrator. As a result, conversion of the signal to a time interval takes place at an earlier stage, eliminating the bridge and the amplifier. The method has the same advantages as the dual-slope method and several additional ones. The fractional change in the transducers is obtained as the ratio of the difference and sum of two time periods. As a result, the converter does not need an accurate voltage reference. In addition, errors due to offset in the integrating amplifier are eliminated.
25 citations
27 Mar 2006
TL;DR: In this paper, a switched capacitor, triple slope digital converter suitable for differential capacitive sensors is presented, which is dependent only on a pair of d.c. reference voltages and the clock frequency.
Abstract: A high accuracy switched capacitor, triple slope digital converter suitable for differential capacitive sensors is presented. The proposed technique accepts differential capacitive sensors possessing either linear or inverse characteristics and provides a linear capacitance to digital conversion. The output is dependent only on a pair of d.c. reference voltages and the clock frequency. Detailed analysis of the proposed scheme establishes that the sensitivity of the scheme to parameter variations is minimal. A prototype implemented and tested for a typical differential capacitive transducer of full-scale ±250 pF gave a worst-case error less than 0.05%.
23 citations
05 May 2009
TL;DR: A direct digital converter that provides a digital output, proportional to the measurand being sensed by a single active element resistive sensor is presented and a high level of linearity and accuracy is achieved.
Abstract: A direct digital converter that provides a digital output, proportional to the measurand being sensed by a single active element resistive sensor is presented in this paper. To accomplish this task, the structure and the switching sequence of a conventional dual slope, analog to digital converter (DSADC) is appropriately altered so that the altered DSADC accepts the resistance of the sensor as an integral part and provides a digital output that is linearly proportional to the physical quantity being sensed by the resistive sensor. Since the output of the dual slope resistance to digital converter (DSRDC) is dictated only by the magnitudes of a pair of DC reference voltages, a fixed value resistor and the transformation constant of the sensor, the error in the output is minimal. Hence, a high level of linearity and accuracy is achieved. Simulation studies establish the efficacy of the proposed scheme.
19 citations