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Journal ArticleDOI

A Direct Digital Readout Circuit for Impedance Sensors

TL;DR: The proposed impedance-to-digital converter is based on a dual-slope technique, and hence provides high accuracy and immunity to noise and interference, and a prototype of the proposed IDC has been developed and tested in the laboratory.
Abstract: A new, simple and high-accuracy impedance-to-digital converter (IDC) is proposed in this paper. Conventionally, the parameters of sensors that can be modeled using a parallel combination of a capacitor ( ${C}$ ) and a resistor ( ${R}$ ) are measured using ac bridges, excited from a sinusoidal source. Recently, with the widespread use of digital systems in instrumentation, capacitance-to-digital converters and resistance-to-digital converters gained a lot of importance. An IDC that accepts sensors having ${C}$ and ${R}$ in parallel and provides digital outputs directly proportional to the ${C}$ and ${R}$ values is presented in this paper. This can be used not only for sensors whose ${C}$ and ${R}$ values vary with the measurand but also when ${C}$ or ${R}$ of a sensor needs to be measured keeping the output not affected by parasitic ${R}$ or ${C}$ present in parallel with the sensing element. Another application of the IDC is in the measurement of the dissipation factor of dielectric materials. The proposed IDC is based on a dual-slope technique, and hence provides high accuracy and immunity to noise and interference. A prototype of the proposed IDC has been developed and tested in the laboratory. Accuracy of the prototype IDC developed was 0.15% for the measurement of ${C}$ and 0.04% for the measurement of ${R}$ . The total conversion time of the prototype converter developed is 3 s, and its total power dissipation is 175.8 mW. The IDC was also interfaced with a polymer-based impedance humidity sensor, measured its ${C}$ and ${R}$ values for a range of humidity, computed the humidity, and compared its performance with another instrument, showing the practicality of the proposed IDC.
Citations
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Journal ArticleDOI
TL;DR: In this article, a novel humidity sensor was fabricated based on a polysquaraine (PMPS), which is of resonance-stabilized zwitterionic structure, and the response/recovery time is as short as 3/16 s, comparable to that of most commercial humidity sensors.
Abstract: Various materials have been successfully applied in commercial humidity sensors, but their response/recovery time and sensitivity need to be improved. In this paper, a novel humidity sensor was fabricated based on a polysquaraine (PMPS), which is of resonance-stabilized zwitterionic structure. Relative humidity (RH) in the range of 33–95% was able to determine by testing the impedance response at room temperature (25 °C). The variation of impedance is greater than four orders of magnitude, the highest among all conjugated polymer materials. The response/recovery time is as short as 3/16 s, comparable to that of most commercial humidity sensors. Electrical doping and hydronium transportation are attributed to the impedance change. The results indicate that polysquaraines may be promising materials in humidity sensing.

44 citations

Journal ArticleDOI
TL;DR: In this article, a simple and accurate impedance measurement technique (IMT) for wide range lossy capacitive sensor is proposed, which is based on the separation of in-phase and quadrature components.
Abstract: In this paper, a new, simple and accurate impedance measurement technique (IMT) for wide range lossy capacitive sensor is proposed. The proposed technique accepts sensors having capacitance ‘Cx’ with lossy resistance ‘Rx’ in parallel. The proposed IMT is based on the separation of in-phase and quadrature components, which is achieved by using phase to time converter. For comparative study, two circuit configurations are proposed. In first proposed solution, the sensor parameters are measured by separating the real and imaginary part of the output electrical signal. In the second proposed configuration, the measurement range is enhanced using an auto-balancing approach, which is achieved by monitoring phase difference between input and output voltages. Experimental evaluation of the proposed configurations reveals that the first configuration is able to estimate the sensor capacitance in the range 200–1200 pF and lossy resistance in the range of 100 kΩ–1.2 MΩ with a maximum error of 6%. The second configuration exhibits an enhanced range of 100–2000 pF for sensor capacitance and 33 kΩ–3 MΩ for lossy resistance with a maximum error of 5%. The IMT was interfaced with a fabricated γ-Al2O3 based impedance humidity sensor, measured its Cx (70 pF–800 pF) and Rx (35 kΩ–4 MΩ) at different concentration of humidity, calculated the humidity, and compared its performance with existing techniques, showing the practicality of the proposed IMT.

43 citations

Journal ArticleDOI
TL;DR: The prototype developed has the option to easily adjust the sensitivity and operating range, depending on the application, and is based on the measurement of quadrature and in-phase components of the signal.
Abstract: This paper presents a low-cost interface circuit for lossy capacitive sensors. Most of the capacitive sensors are lossy in nature, where the resistance value of the sensor significantly varies along with the capacitance value. Accurate measurement of those values of a lossy capacitive sensor is a challenging task. This paper deals with the development of an electronic interface circuit for such a capacitive sensor. The circuit is based on the measurement of quadrature and in-phase components of the signal. To extract the actual value of the capacitance and the resistance, an average of the quadrature and the in-phase components of output is required. This is implemented using a microcontroller and provides flexibility in averaging (e.g., adjustable length of data to be processed). A PCB of the circuit has been fabricated and tested in the laboratory using capacitors and resistors with known values. The accuracy of the circuit was better than 0.6% and −2.2% for the measurement of capacitance and resistance, respectively. Also, the circuit is highly linear (FS nonlinearity of 0.32%) for a wide range of capacitance measurement (162 pF–3.680 nF). To confirm the effectiveness of the circuit, it was interfaced to a lossy capacitive humidity sensor and another capacitive transducer to measure the dielectric constants of edible oils. The results were compared with a precision impedance analyzer (Agilent 4294A); the maximum relative error was noted as ±1.6% in the measurement of permittivity values of edible oil. The prototype developed has the option to easily adjust the sensitivity and operating range, depending on the application.

36 citations


Cites background from "A Direct Digital Readout Circuit fo..."

  • ...In [16] and [17], an impedance to digital convertor has been proposed to estimate the value of both Rs and Cs with high accuracy, but its working range is limited to 100–200 pF for Cs and 700....

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Journal ArticleDOI
TL;DR: An in-vehicle system prototype supporting combined monitoring services of air-quality and healthcare was integrated into a steering wheel cover and experimentally verified to provide real-time measurement of three environmental sensor signals and two healthcare physiological signals with the results displayed on a smartphone.
Abstract: This paper presents a reconfigurable multisensor mobile interface architecture that is applicable to heterogeneous sensor applications and also easy to generate new types of combined services. The multisensor interface attributes compactness and flexibility to reconfigurable readout integrated circuits (ROICs) and migration of signal processing and computation burdens from a sensor tag to a smartphone. Two reconfigurable ROICs which were designed and fabricated in a 0.18-μm CMOS process generate raw digital data from environmental and healthcare sensors. Their detected raw data are wirelessly sent to the smartphone where real-time calibration and postprocessing are performed optimally for each sensor. In an application to industrial systems, an in-vehicle system prototype supporting combined monitoring services of air-quality and healthcare was integrated into a steering wheel cover and experimentally verified to provide real-time measurement of three environmental sensor signals and two healthcare physiological signals with the results displayed on a smartphone.

32 citations


Cites background from "A Direct Digital Readout Circuit fo..."

  • ...A multitype ROIC for resistive and capacitive sensors was reported as in [21], but it did not include the CDS function....

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References
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Book
01 Aug 1996
TL;DR: Capacitive sensors in Silicon Technology as discussed by the authors have been shown to have high dielectric properties of various materials, including electret microphones, acceleration sensors, and sensors with different types of connectors.
Abstract: Preface Introduction Electrostatics Capacitive Sensor Basics Circuit Basics APPLICATIONS Capacitive Micrometers Proximity Detectors Motion Encoders Multiple Plate Systems Miscellaneous Sensors DESIGN Circuits and Components Switched Capacitor Techniques Noise and Stability Hazards PRODUCTS Electret Microphone Accelerometer StudSensor Proximity Detector Vernier Caliper Graphic Input Tablet Camera Positioner Digital Level References Appendix 1--Capacitive Sensors in Silicon Technology Appendix 2--Dielectric Properties of Various Materials Index

695 citations


"A Direct Digital Readout Circuit fo..." refers background in this paper

  • ...2361552 Electrical equivalent circuit of simplified model of a capacitive sensor, with dielectric loss, consists of a capacitance (C1) and a resistance (R1) in parallel [1], [14]....

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  • ...CAPACITIVE sensors are often used in a variety of scientific and industrial applications owing to their benefits such as low power consumption, high sensitivity, and accuracy [1], [2]....

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Book
17 Aug 1993
TL;DR: Signal Conditioning for Resistive Sensors Reactance Variation and Electromagnetic Sensors and Signals for Self-Generating Sensors Signal conditioning for self-Generation Sensors Digital Sensors Telemetry and Data Acquisition.
Abstract: Resistive Sensors Signal Conditioning for Resistive Sensors Reactance Variation and Electromagnetic Sensors Signal Conditioning for Reactance Variation Sensors Generating Sensors Signal Conditioning for Self-Generating Sensors Digital Sensors Other Sensing Methods Telemetry and Data Acquisition General Bibliography Appendix Index.

432 citations


"A Direct Digital Readout Circuit fo..." refers background or methods in this paper

  • ...CAPACITIVE sensors are often used in a variety of scientific and industrial applications owing to their benefits such as low power consumption, high sensitivity, and accuracy [1], [2]....

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  • ...In most of the aforementioned applications, a sinusoidal source at an appropriate frequency is employed as excitation signal and synchronous demodulationbased schemes are used to measure the output signal from the sensor, to achieve high noise immunity [2], [12], [13]....

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Journal ArticleDOI
TL;DR: In this paper, different designs of sensing electronics for ECT systems are presented and the advantages and disadvantages compared and the capacitances can be measured by high-accuracy self balancing circuits without standing value compensation.
Abstract: Electrical capacitance tomography (ECT) was one of the techniques which were firstly developed for process tomography (PT) Two types of capacitance measuring circuits are the most suitable for the use in ECT systems - the charge/discharge circuit and the AC-based circuit - because of their immunity to stray capacitance Since the standing capacitances involved are relatively large and the capacitance changes to be measured are very small, the standing values need to be cancelled by DC offset compensation or AC feedback compensation Alternatively, the capacitances can be measured by high-accuracy self-balancing circuits without standing value compensation In this paper different designs of sensing electronics for ECT systems are presented and the advantages and disadvantages compared

248 citations


Additional excerpts

  • ...In [21], a sinusoidal excitation is employed....

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01 Jan 2016

206 citations


"A Direct Digital Readout Circuit fo..." refers background or methods in this paper

  • ...The slew rate (SR) of the opamps OA1 and OA2 should be such that√ 2Vo1 f ≤ S R/2π [30]....

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  • ...pole model [30], [31] of the opamp with open loop transfer function G(s) = Ao/(1 + s/ωa) can be used, where ωa is the dominant pole frequency and Ao is the open loop dc gain [31]....

    [...]

  • ...Thus, opamps with suitable compensation techniques [30], [31] or opamps with higher GBP should be employed to keep the error within the limits....

    [...]

  • ...The slew rate (SR) of the opamps OA1 and OA2 should be such that √ 2Vo1 f ≤ S R/2π [30]....

    [...]

Journal ArticleDOI
TL;DR: A fully integrated CMOS humidity sensor for a smart RFID sensor platform that provides a resolution of 0.05% RH in the range from 30% RH to 100% RH while consuming only 8.3 nJ per measurement, which is an order- of-magnitude less energy than the state-of-the-art.
Abstract: This paper presents a fully integrated CMOS humidity sensor for a smart RFID sensor platform. The sensing element is a CMOS-compatible capacitive humidity sensor, which consists of top-metal finger-structure electrodes covered by a humidity-sensitive polyimide layer. Its humidity-sensitive capacitance is digitized by an energy-efficient capacitance-to-digital converter (CDC) based on a third-order delta-sigma modulator. This CDC employs current-efficient operational transconductance amplifiers based on current-starved cascoded inverters, whose limited output swing is accommodated by employing a feedforward loop-filter topology. A programmable offset capacitor is included to remove the sensor's baseline capacitance and thus reduce the required dynamic range. To reduce offset errors due to charge injection of the switches, the entire system is auto-zeroed. The proposed humidity sensor has been realized in a 0.16- μm CMOS technology. Measurement results show that the CDC performs a 12.5-bit capacitance-to-digital conversion in a measurement time of 0.8 ms, while consuming only 8.6 μA from a 1.2-V supply. This corresponds to a state-of-the-art figure-of-merit of 1.4 pJ/conversion-step. Combined with the co-integrated humidity sensing element, it provides a resolution of 0.05% RH in the range from 30% RH to 100% RH while consuming only 8.3 nJ per measurement, which is an order-of-magnitude less energy than the state-of-the-art.

125 citations