Indian Institute of Technology Palakkad&nbsp;(IIT Palakkad or IIT PKD) is a public autonomous&nbsp;engineering&nbsp;and&nbsp;research&nbsp;institute located in&nbsp;Palakkad,&nbsp;Kerala. It was&nbsp;one of the five new&nbsp;IITs&nbsp;proposed in the&nbsp;2014 Union budget of India. The campus was inaugurated on 3 August 2015. The institute has 94 faculty, 978 students, and 63 non-teaching staffs.

IT Palakkad currently offers four-year Bachelor of Technology (B.Tech) and two years MS programmes in 8 different engineering disciplines including&nbsp;Computer Science, Electrical, Mechanical, Civil among others.

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IIT Palakkad

This paper presents a new capacitance-to-frequency converter (CFC) with high linearity and accuracy. In the CFC, the capacitance-to-frequency conversion is achieved using a negative feedback mechanism. In the feedback, the output frequency controls the charge injected by a switched-capacitor (SC) network such that the difference error is automatically minimized. The feedback mechanism ensures that the final output is insensitive to the nonlinearity errors of the units employed to realize the forward path, namely, a capacitance-to-voltage converter and a voltage-to-frequency converter. A simple error correction mechanism employed ensures that the digital output obtained is insensitive to the number of nonideal circuit parameters. The proposed converter uses a dc reference voltage for the excitation and helps to achieve high accuracy. A prototype of the improved CFC has been developed and tested for sensor capacitance Cx in the range of 5-25 pF. A prototype of the conventional open-loop CFC was also developed, and the linearity has been evaluated. The proposed closed-loop approach has lower (0.1%) nonlinearity error compared to the conventional CFC (0.8%). This improvement is achieved without the use of any error-compensating schemes, and hence the complexity level of the system remains the same as that of any typical CFC. The response time of the CFC designed is about 400 μs for a 5-25 pF step change in Cx. The results obtained from the prototype CFC confirmed its usefulness. © 2018 IEEE.

Department of Electrical Engineering

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IEEE Transactions on Instrumentation and Measurement

An Improved Closed-Loop Switched Capacitor Capacitance-to-Frequency Converter and Its Evaluation

A capacitance-to-digital converter (CDC) designed to possess negligible sensitivity to non-ideal circuit parameters is presented in this paper. The scheme is based on switched capacitor integrating technique and the conversion process is such that the final output is fundamentally insensitive to leakage resistance and stray capacitance of the sensor, offset voltage and bias current of the opamp, delay, offset voltage, and bias current of the comparator, leakage current, delay, and charge injection of the switches employed, and so on. Such a characteristic is highly useful for precision measurement. The proposed CDC achieves it without any special compensating circuits, unlike some of the existing CDCs that partially meet the above feature. The performance of the CDC has been experimentally evaluated. Results show high insensitivity to the non-ideal circuit parameters. In addition, the worst case non-linearity error of the prototype CDC was found to be less than 0.1%, when tested for a range of 10 to 400 pF. © 2001-2012 IEEE.

IEEE Sensors Journal

A robust switched-capacitor CDC

In this paper, a new digitizer, which accurately provides the values of the change in the capacitor Cx and resistor Rx of a parallel R-C sensor, is presented. Conventional measurement schemes for parallel R-C sensors require a precision sinusoidal excitation, followed by a signal conditioner, a demodulator and an ADC. This increases the cost and complexity of the scheme. Hence, a dc excitation and an ADC modified to measure Rx and Cx directly is preferred, by the design engineers. But, such a scheme has not been reported. Another challenge is the low-modulation nature of such sensors, i.e., the change in resistance ΔR and capacitance ΔC can be very small compared with the nominal values R0 and C0 of the sensor. This introduces a large offset in the digital output, leading to an inefficient conversion. The proposed digitizer employs a dc excitation and provides accurate digital values of change ΔR in Rx and ΔC in Cx of the sensor. The digitizer employs a simple, but effective automatic calibration, with the help of an improved switched capacitor controlled voltage and obtains an output independent of the nominal values (R0 and C0) of the sensor leading to an efficient conversion compared with the existing schemes. A detailed analysis of the sources of errors affecting the output of the digitizer has been conducted. A prototype of the proposed digitizer has been developed and tested in the laboratory for a wide range of R0 and C0. The results show that the output of the proposed digitizer is independent of the R0 and C0 and can accurately measure the ΔR and ΔC without any cross-sensitivity. © 2017 IEEE.

A Switched-Capacitor Circuit-Based Digitizer for Efficient Interfacing of Parallel R-C Sensors

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. © 2017 IEEE.

A resistive sensor readout circuit with intrinsic insensitivity to circuit parameters and its evaluation

In this paper, a novel Capacitance-to-Frequency Converter (CFC) with high linearity is presented. In the CFC, the capacitance to frequency conversion is obtained using a negative feedback mechanism. In this feedback, the frequency of the output controls the current delivered by a Switched-Capacitor (SC) network such that the difference error is automatically minimized. The proposed converter uses a dc reference voltage for the excitation and achieves high accuracy. The feedback mechanism ensures that the final output is insensitive to the linearity errors of the units employed to realize the forward path; namely a capacitance-to-voltage converter and a voltage-to-frequency converter. A prototype of the proposed CFC has been developed. The prototype was tested for sensor capacitance Cx varied from 5 pF to 25 pF. A prototype of the conventional CFC that operates in an open-loop mechanism was also developed and the linearity error was evaluated. It has been noted that the proposed closed-loop approach, reduces the worst-case nonlinearity error from 0.8% to 0.1%. This improvement is achieved without the use of any error compensating circuitries, and hence complexity level of the system remains same as a typical CFC. The prototype CFC has an update rate of 10 kS/s. The results obtained from the CFC confirmed its usefulness. © 2017 IEEE.

I2MTC 2017 - 2017 IEEE International Instrumentation and Measurement Technology Conference, Proceedings

A novel closed-loop SC Capacitance-to-Frequency Converter with high linearity

A new Resistance-to-Digital Converter (RDC) suitable for single element resistive sensors is presented in this paper. The proposed scheme is based on a relaxation oscillator circuit, which along with a timer-counter that measures the time intervals of oscillations, provides digital output proportional to the resistance of the sensor. In most of the existing RDCs, the output characteristic has gain, offset and non-linearity errors owing to various circuit parameters and their drift in the measurement unit. The output of the proposed RDC has a special nature, by the design of the measurement method, that it is not a function of the circuit parameters such as offset voltages and bias currents of the opamps and comparators used, gain of various units employed, ON-resistance of the switches, value or mismatch in the magnitudes of the reference voltages employed, etc. Such a scheme will be useful for high accuracy measurements, even in circumstances where the above-mentioned parameters may vary or drift, due to variation in the measurement environment, say, large variation in temperature. A prototype of the proposed RDC has been developed in the laboratory and the performance has been tested under various conditions. The output was found to be linear with a worst-case non-linearity of 0.06 % As expected, the sensitive of the output of the prototype RDC to various circuit parameters was found to be negligible. © 2016 IEEE.

Conference Record - IEEE Instrumentation and Measurement Technology Conference

A Resistance-to-Digital Converter possessing exceptional insensitivity to circuit parameters

In this paper, a new and high accuracy, dual-purpose Direct-Digital Converter (DDC) is presented. The proposed Switched-Capacitor (SC) DDC can be used to interface sensors whose electrical equivalent is (a) a capacitor Cx or (b) a resistor Rx or (c) Cx and Rx in parallel. Irrespective of (a)-(c), the DDC gives digital outputs proportional to Cx and Rx of the sensor. Capacitance-to-Digital Converters (CDC) and Resistance-to-Digital Converters (RDC) have been reported earlier, but no accurate dual-purpose DDC has been reported. In comparison with most of the CDCs/RDCs, the DDC presented uses no noticeable additional hardware. In the DDC, the conversion is obtained based on a SC dual-slope technique, which guarantees high immunity to interference. The DDC uses a dc reference voltage for excitation and helps to achieve high accuracy. A prototype of the proposed DDC has been developed. The prototype was tested for Rx from 50 kΩ to 1 MΩ and Cx from 50 pF to 250 pF. The results obtained from the DDC confirmed its usefulness. © 2016 IEEE.

A direct-digital interface circuit for sensors representable using parallel R-C model

A novel Dual-Slope Resistance-to-Digital Converter (DSRDC) suitable for single element resistive sensors is presented in this paper. The digital output of the converter is directly proportional to the measurand and is insensitive to the nominal value of resistance, Ro, of the sensor. The choice of fixed resistance employed in a typical DSRDC has been made to be independent of Ro and the constraints on its accuracy have been relaxed. This makes the Resistance-to-Digital Converter versatile, in a manner that it can be easily interfaced with a wide range of resistive sensors having different values of Ro. This task was accomplished by employing an automatic calibration technique, wherein, the reference voltage is digitally adjusted by a Switched Capacitor Controlled Voltage Source (SCCVS). A prototype DSRDC was developed and tested against various values of Ro, which were in-turn emulated using known resistances of values ranging from 25 kü to 200 kü. The worst case error in reading was observed to be less than 0.65 %. © 2016 IEEE.

SAS 2016 - Sensors Applications Symposium, Proceedings

A modified RDC with an auto-adjustable SC source enabled auto-calibration scheme

A new capacitance-to-digital converter (CDC) that gives a digital output proportional to the measurand kx, independent of its nominal capacitance, is reported in this paper. Various CDCs are available in the market, but their output is a function of the nominal value C0 of the sensor. Thus, a manual correction is required in the output, whenever a new capacitive sensor is interfaced to such CDCs. Moreover, the C0 of the sensors is usually a large value compared with the change in capacitance due to kx. Thus, in a typical CDC, a large percentage of the output counts/bits is used to measure and represent the C0 leading to an underutilization of the hardware as far as the measurement of kx is concerned. The proposed CDC uses a new automatic calibration (AC), employing a switched-capacitor (SC) circuit-based voltage source in a feedback topology, and provides an output independent of the C0 of the sensor employed. The proposed CDC is based on an SC dual-slope technique and possesses the advantages of the dual-slope conversion method. The CDC circuit is designed such that the entire full scale can be used for representing the change in the kx. In addition to this advantage, the AC helps to remove the dependence on the accuracy of the reference capacitor employed in the CDC. A detailed analysis of the effect of various sources of errors in the CDC has been conducted and presented in this paper. A prototype of the proposed CDC has been developed and tested. The results obtained show that the output of the CDC is not a function of the C0 (C0 varied from 60 pF to 1.46 nF) of the sensors interfaced. © 2015 IEEE.

An Easy-to-Interface CDC With an Efficient Automatic Calibration

A capacitance-to-digital converter (CDC) that gives a digital value proportional to the change in the capacitance of a sensor, independent of its nominal capacitance, is presented in this paper. The CDC presented is suitable for single element capacitive sensors. For most of the CDCs, available in the market, the output depends on the nominal value of the sensor. Thus, a manual intervention for appropriate correction in the output is required whenever a new sensor is connected to such CDCs. The proposed CDC uses a simple automatic calibration, employing a digitally controlled reference voltage in a feedback topology, and provides an output independent of the nominal value of the sensor employed. This automatic calibration also removes the dependence on the accuracy of the absolute value of reference capacitor, in the final output. The proposed CDC is based on a switched-capacitor dual-slope technique and possesses the advantages of the dual-slope conversion method. A prototype CDC has been developed and the test results are presented. The results obtained show that the output of the proposed converter is not a function of the nominal capacitance of the sensor for a wide range (50 pF to 1.15 nF). For this range, the worst error noted from the prototype CDC was less than 0.65 %. © 2015 IEEE.