2015 6th International Workshop on Advances in Sensors and Interfaces (IWASI), 2015
In this paper we present an analog electronic interface, developed in an integrated standard CMOS... more In this paper we present an analog electronic interface, developed in an integrated standard CMOS technology, for differential capacitive sensors. In particular, the two cases of hyperbolic and linear capacitive behavior have been considered. The capacitive evaluation can be done by the design and characterization of a suitable electronic circuit which determines the measurand variations through the reading of a voltage. This approach has shown high accuracy as well as other solutions reported in the literature where the capacitances are typically converted into a frequency. The front-end has been designed in a standard CMOS technology (AMS 0.35 um) to work at dual supply voltages (1.65 V each), so to be suitable for low-cost portable applications. Spice simulations on the designed integrated solution and experimental results using a discrete-component prototype have shown a reduced absolute percentage error (lower than 1% and 3.5 %, respectively), if compared to theoretical expressions. Sensitivity and resolution on a practical case study of the sensor/interface system are also given, showing very satisfactory values.
In this paper, a new realization of electronically controllable positive and negative floating ca... more In this paper, a new realization of electronically controllable positive and negative floating capacitor multiplier (±C) is presented. The peculiarity of the presented topology is that, for the first time, it implements a floating equivalent capacitor between its two input terminals, rather than a grounded one. To achieve the best performance, we simultaneously use the advantages provided by the current conveyor and its dual circuit, the voltage conveyor. The proposed topology is resistor free and employs one dual-output second-generation voltage conveyor (VCII±) and one electronically tunable differential voltage current conveyor (E-DVCC) as active building blocks (ABBs) and a single grounded capacitor. The value of the simulated capacitor is controlled by means of a control voltage VC which is used to control the current gain between X and Z terminals of E-DVCC. The circuit is free from any matching condition. A complete non-ideal analysis by considering parasitic impedances as we...
This study reviews second-generation voltage conveyor (VCII)-based read-out circuits for sensors ... more This study reviews second-generation voltage conveyor (VCII)-based read-out circuits for sensors and bioelectrical signal conditioning from existing literature. VCII is the dual circuit of a second-generation current conveyor (CCII), which provides the possibility of processing signals in the current domain while providing output signals in the voltage form. The scope of this paper is to discuss the benefits and opportunities of new VCII-based read-out circuits over traditional ones and bioelectrical signals. The achieved main benefits compared to conventional circuits are the simpler read-out circuits, producing an output signal in a voltage form that can be directly used, improved accuracy, possibility of gain adjustment using a single grounded resistor, and the possibility of connecting several SiPM sensors to the readout circuit. The circuits studied in this paper include VCII- based read-out circuits suitable for all types of sensors configured in the current-mode Wheatstone br...
2017 13th Conference on Ph.D. Research in Microelectronics and Electronics (PRIME), 2017
This work describes an analog electronic interface, based on a modified De Sauty AC bridge, perfo... more This work describes an analog electronic interface, based on a modified De Sauty AC bridge, performing a differential capacitive sensor estimation. A suitable feedback loop tunes a Voltage Controlled Resistor to balance the bridge. The electronic circuit has been designed in a standard integrated CMOS technology (AMS 0.35μm) with a low supply voltage (±1.5 V) and a reduced power consumption (lower than 4mW). PSpice simulation results show a very good agreement with theoretical expectations. The output voltage accuracy shows a 0.03V maximum absolute error for a range of ±50% of sensor variations from its baseline value. Very small baseline values are allowed (tens of μF).
Journal of Communications Software and Systems, 2018
In this work we present a combined 90/900 MHz Energy Harvesting Architecture for IoT device power... more In this work we present a combined 90/900 MHz Energy Harvesting Architecture for IoT device power assisting. The harvester takes advantages from a dedicated diplexer and a power manager for battery life enhancement purposes. The system has been optimized in the 900 MHz frequency range by analyzing a probabilistic approach used for modeling the possible amount of Global System for Mobile communication (GSM) energy that could be harvested while a fixed power downlink scenario has been adopted for the 90MHz band. A preliminary IC system with a 0.18μm CMOS SMIC technology has been designed and optimized at 90 and 900 MHz while discrete element board, to be integrated with the proposed IC, with commercial components has been developed and tested. Concerning simulation results on the IC design they have confirmed that the integrated system handles an incoming power typically ranging from-25 dBm to 5 dBm by rectifying the variable input signals into a DC voltage source with an average 50% efficiency. Keywords-Radio frequency energy harvesting, rectifiers, probabilistic modelling, dual band energy harvesting. I. INTRODUCTION Nowadays energy recovery from environmental power sources is an innovative and appealing way to capture and store energy for small, wireless and autonomous devices commonly used in wearable electronics, low voltage or low power circuit and systems, and, more and more, on Wireless Sensor Network (WSN) systems [1-5]. Energy Harvesting (EH) is the process of scavenging ambient energy from sources in the surrounding environment. It is an attractive method for overcoming the energy limitations of conventional battery powered wireless devices. As a consequence, efficient harvesters can potentially lead to significant reduction in the costs associated with replacing batteries periodically. The best-known EH collectors are large solar panels and wind generators, which have become major alternative energy
Journal of Communications Software and Systems, 2017
In this work we present an IC architecture for RF energy harvesting. The system has been designed... more In this work we present an IC architecture for RF energy harvesting. The system has been designed with a 0.18μm CMOS SMIC technology and optimized at 900MHz. Simulation results have confirmed that the integrated system handles an incoming power typically ranging from -25 dBm to 20 dBm by rectifying the variable input signals into a DC voltage source with an overall efficiency up to 50%. The chip area estimation for the proposed system is as low as 3x3mm2.
In this work, we present an innovative low cost sensor and algorithm for the monitoring and measu... more In this work, we present an innovative low cost sensor and algorithm for the monitoring and measurement of solar irradiance. This parameter is usually estimated using pyranometers, often based on thermopile. They are quite expensive, also because need additional hardware for data acquisition and manipulation as well as non-negligible installation costs. The system architecture and novel algorithm here proposed employ small PhotoVoltaic (PV) cells and a digital sensor interface. Moreover, the logic section permits to tilt the sensor allowing to track the sun with improved accuracy.
An integrated pulseoximeter/heartbeat rate detector is herewith described. The ready-to-use capab... more An integrated pulseoximeter/heartbeat rate detector is herewith described. The ready-to-use capability and its easy portability make the device a reliable, non-intrusive detector to be used in a large amount of applications (medical, domestic monitoring, sport scenarios). Both the blood oxygen percentage detection (i.e. pulsoximetry) and heartbeat rate monitoring are obtained thanks to a light-sensible set of diodes and receivers, by opportunely evaluating the emitted and received power light ratio through the body, using a standard technique. Test results have demonstrated that a simple 10-bit A/D converter can display both the O2 blood concentration percentage and the heartbeat rate accurately.
A new analog lock-in amplifier for automatic measurements of very small and noisy signals is prop... more A new analog lock-in amplifier for automatic measurements of very small and noisy signals is proposed here. The integrated system, which is particularly suitable for the accurate detection in sensor applications, performs continuously the relative phase alignment and the frequency tuning of input and reference signals through automatic operations ensured by suitable feedbacks. The complete structure of this amplifier has been implemented both as a PCB, with discrete commercial components, and as an ASIC, fabricated in AMS 0.35 μm standard CMOS technology. The system has been optimized to operate in the operating frequency range (2.5 ÷ 25) Hz, so resulting suitable for different sensor applications. Conducted measurements, also employing commercial resistive gas sensors for the ethylene glycol revelation, have demonstrated the system validity and its satisfactory performances in the detection of noisy signal amplitudes, also down to tens of nV. Moreover, with respect to a simpler resistive voltage divider, typically used as a basic sensor interface, the resolution improvement provided by the proposed lock-in allows a theoretical concentration detection in the order of tens of ppb.
A new oscillating circuit is proposed to estimate resistance and parallel parasitic capacitance o... more A new oscillating circuit is proposed to estimate resistance and parallel parasitic capacitance of chemical sensors. The circuit is able to reveal resistance in a wide range, from tens of k Omega to over than 100 G Omega. Experimental results of a discrete board prototype confirm the very good performance of post-layout simulation tests concerning the CMOS integrated implementation.
2009 Ph.D. Research in Microelectronics and Electronics, PRIME 2009, 2009
In this paper we present a novel internal architecture of low-voltage and low-power positive seco... more In this paper we present a novel internal architecture of low-voltage and low-power positive second-generation current conveyor (CCII+). The proposed internal circuit topology, designed in standard CMOS technology (AMS 0.35 ¿m), employs an n-type differential pair as input stage, while a cascoded push-pull configuration implements a very high impedance output stage. A degenerated nMOS common drain topology reduces X node impedance. The choice of internal CCII+ architecture, concerning both its stage architecture and transistor sizes, has been made in the direction of designing a quasi-ideal CCII+ in terms of parasitic components at its terminals. The developed CCII+ operates at low supply voltages of ±1 V with a total power consumption of about 300 ¿W, so it is suitable for general purpose portable applications. It has been also characterized implementing well-known applications, both in time and frequency domains, such as signal processing circuits and impedance simulators.
2007 IEEE International Symposium on Circuits and Systems, 2007
In this paper we describe an approach for the design of high-accuracy, high-precision, current mo... more In this paper we describe an approach for the design of high-accuracy, high-precision, current mode amplifiers. These circuits take advantage of dynamic element matching (DEM) for compensating the input offset and /f noise voltages of the nominally identical (source-coupled) transistor pairs in a second generation current conveyor (CCII). In comparison with high-accuracy, high-precision op amp based amplifiers, the proposed approach is more convenient if the gain of the op amp may not be very high, e.g. due to short channel effects.
Parallel arrays of well aligned crack-free N-doped and undoped TiO 2 nanofibers (3-4 mm long, 300... more Parallel arrays of well aligned crack-free N-doped and undoped TiO 2 nanofibers (3-4 mm long, 300-500 nm diameter) have been deposited by near field electrospinning (NFES) technique on Si 3 N 4 substrates with interdigitated Pt electrodes and annealed at 400 • C for 1 h. Anatase TiO 2 with crystallites' size of approximately 12 nm have been prepared and characterized by XRD, SEM, TEM and XPS techniques. Experimental measurements have been conducted through an ad hoc analog integrated resistive sensor interface, based on an oscillating circuit, fabricated in a 0.35 m standard CMOS technology. Gas response to NO 2 in the range 1-10 ppm and 100-300 • C operating temperature (OT) has shown best practical sensor sensitivity (S = R G /R A) at a relatively low OT (150 • C) and detection limits down to 1 ppm gas. Nitrogen doping at N:Ti 1:1 atomic ratio has been proposed in order to decrease the intrinsic resistance of TiO 2 , thus enabling better signal to noise ratio of the electrical response.
IEEE Transactions on Instrumentation and Measurement, 2010
The main issue concerning metal oxide (MOX) gas sensors is mostly related to the wide range of re... more The main issue concerning metal oxide (MOX) gas sensors is mostly related to the wide range of resistive values that the sensors can show. In addition, some sensors could have baseline resistive values up to tens of gigohms. To avoid the use of expensive picoammeters or the use of circuits adopting scaling factors, different solutions have recently been proposed, exploiting the resistance-to-time conversion (RTC) technique. They show good linearity and are suitable for the integration in a chip together with the elaboration unit, but they may require long measurement time (tens of seconds) if high resistance values need to be estimated. In addition, they may suffer the influence of a sensor parasitic capacitance, in parallel with the resistive component. In this paper, a new method is proposed to reduce the measuring time, keeping the advantages offered by the RTC approach and including a parasitic capacitance estimation feature. Particularly, an effective architecture, based on moving thresholds, has been proposed, simulated, and experimentally tested with commercial resistors (values between 1 MΩ and 100 GΩ) and capacitors (values between 1 and 47 pF). Finally, a fast sensor transient, due to a rapid change in the heating power, has been acquired with the proposed instrument and compared with a similar transient analyzed with a classical RTC approach. This test has shown the applicability of the interface for solutions requiring detailed information of the sensor response, such as the characterization of new sensors (e.g., nanowires) or the behavior analysis during nonstandard thermal profiles. Index Terms-Fast transient analysis, high resistive sensor, low measuring time, parasitic capacitance estimation, wide-range resistances. I. INTRODUCTION M ETAL oxide (MOX) gas sensors are often used due to their advantages, namely, good sensitivity to relevant gases, low production cost, and small size. They react to the presence of the gas by varying the conductivity; therefore, they can be considered as resistive sensors. In addition, due to the particular processes used to implement the sensor and to the Manuscript
IEEE Transactions on Circuits and Systems II: Express Briefs, 2008
In low-voltage, deep sub-m analog CMOS circuits, the accuracy and precision can be limited by the... more In low-voltage, deep sub-m analog CMOS circuits, the accuracy and precision can be limited by the finite gain as well as by the input offset and 1 noise voltages of opamps. Here, we show how to design high-accuracy high-precision CMOS amplifiers by properly applying dynamic element matching to a secondgeneration current conveyor (CCII); if all of the critical, nominally identical transistor pairs are dynamically matched, the resulting amplifier has low residual input offset and noise voltages. When compared with chopper or traditional dynamic element-matching amplifiers, the proposed approach alleviates the tradeoff between output swing and output resistance and is more robust against the finite opamp gain. Transistor-level simulations confirm theoretical results.
ABSTRACT Chemical sensors for gas detection nowadays are widely used in several applications; bas... more ABSTRACT Chemical sensors for gas detection nowadays are widely used in several applications; basically, electrochemical sensors and semiconductor devices are used for this purpose. In both cases, the sensor value estimation is usually implemented as a current measurement and they are often referred as current-output sensors. In this paper, a versatile and low-cost interface circuit for such kind of sensors is presented. The proposed solution is characterized by a wide measurement range, yielding flexibility of use with sensors showing different baseline values. In addition, the fast readout time, on the order of tens of milliseconds, guarantees an accurate acquisition of the sensor data even in presence of fast transients, for example when using sensors operated in pulsed thermal regimes. The front-end works with a single-voltage power supply and furnishes a time-coded digital output signal, thus it is suitable to be directly interfaced to a microcontroller for the management of the measurement process, data elaboration, and presentation. Simplicity and compactness of the electronic interface make possible the integration in a single-chip solution, together with the digital electronics. Reproducibility of the circuit, for applications requiring the simultaneous acquisition of multiple sensors, is furthermore facilitated. The proposed approach has been validated with experimental tests conducted on a discrete component prototype. The system characterization has shown a maximum linearity error in the estimation of the sensor current or resistance of ~ 5% over a measurement range of seven decades; the measurement time is in all the considered input range. Fast thermal transients of different semiconductor sensors for gas sensing have been successfully acquired, demonstrating the validity of the proposed approach. Power dissipation ( at 3.3 V) and the front-end cost ( ~ 10 $) make the presented solution suitable for the employment in low-cost and low-power gas detection system- .
In this paper, we propose a low-voltage (LV) low-power (LP) oscillating circuit suitable for the ... more In this paper, we propose a low-voltage (LV) low-power (LP) oscillating circuit suitable for the read-out of DC-excited resistive gas sensors, based on Second Generation Current Conveyors (CCIIs). This low-cost fully integrable front-end is able to evaluate the resistive behavior of gas sensors, without any preliminary calibration, operating a Resistance to Time ( R-T) conversion and exciting the sensor with
The use of capacitive sensors has advantages in different industrial applications due to their lo... more The use of capacitive sensors has advantages in different industrial applications due to their low cost and low-temperature dependence. In this sense, the current-mode approach by means of second-generation current conveyors (CCIIs) allows for improvements in key features, such as sensitivity and resolution. In this paper, a novel architecture of CCII for differential capacitive sensor interfaces is presented. The proposed topology shows a closed-loop configuration for both the voltage and the current buffer, thus leading to better interface impedances at terminals X and Z. Moreover, a low power consumption of 600 µW was obtained due to class-AB biasing of both buffers, and the inherent drawbacks in terms of linearity under the mismatch of class-AB buffering are overcome by its closed-loop configuration. The advantages of the novel architecture are demonstrated by circuit analysis and simulations; in particular, very good robustness under process, supply voltage and temperature vari...
2015 6th International Workshop on Advances in Sensors and Interfaces (IWASI), 2015
In this paper we present an analog electronic interface, developed in an integrated standard CMOS... more In this paper we present an analog electronic interface, developed in an integrated standard CMOS technology, for differential capacitive sensors. In particular, the two cases of hyperbolic and linear capacitive behavior have been considered. The capacitive evaluation can be done by the design and characterization of a suitable electronic circuit which determines the measurand variations through the reading of a voltage. This approach has shown high accuracy as well as other solutions reported in the literature where the capacitances are typically converted into a frequency. The front-end has been designed in a standard CMOS technology (AMS 0.35 um) to work at dual supply voltages (1.65 V each), so to be suitable for low-cost portable applications. Spice simulations on the designed integrated solution and experimental results using a discrete-component prototype have shown a reduced absolute percentage error (lower than 1% and 3.5 %, respectively), if compared to theoretical expressions. Sensitivity and resolution on a practical case study of the sensor/interface system are also given, showing very satisfactory values.
In this paper, a new realization of electronically controllable positive and negative floating ca... more In this paper, a new realization of electronically controllable positive and negative floating capacitor multiplier (±C) is presented. The peculiarity of the presented topology is that, for the first time, it implements a floating equivalent capacitor between its two input terminals, rather than a grounded one. To achieve the best performance, we simultaneously use the advantages provided by the current conveyor and its dual circuit, the voltage conveyor. The proposed topology is resistor free and employs one dual-output second-generation voltage conveyor (VCII±) and one electronically tunable differential voltage current conveyor (E-DVCC) as active building blocks (ABBs) and a single grounded capacitor. The value of the simulated capacitor is controlled by means of a control voltage VC which is used to control the current gain between X and Z terminals of E-DVCC. The circuit is free from any matching condition. A complete non-ideal analysis by considering parasitic impedances as we...
This study reviews second-generation voltage conveyor (VCII)-based read-out circuits for sensors ... more This study reviews second-generation voltage conveyor (VCII)-based read-out circuits for sensors and bioelectrical signal conditioning from existing literature. VCII is the dual circuit of a second-generation current conveyor (CCII), which provides the possibility of processing signals in the current domain while providing output signals in the voltage form. The scope of this paper is to discuss the benefits and opportunities of new VCII-based read-out circuits over traditional ones and bioelectrical signals. The achieved main benefits compared to conventional circuits are the simpler read-out circuits, producing an output signal in a voltage form that can be directly used, improved accuracy, possibility of gain adjustment using a single grounded resistor, and the possibility of connecting several SiPM sensors to the readout circuit. The circuits studied in this paper include VCII- based read-out circuits suitable for all types of sensors configured in the current-mode Wheatstone br...
2017 13th Conference on Ph.D. Research in Microelectronics and Electronics (PRIME), 2017
This work describes an analog electronic interface, based on a modified De Sauty AC bridge, perfo... more This work describes an analog electronic interface, based on a modified De Sauty AC bridge, performing a differential capacitive sensor estimation. A suitable feedback loop tunes a Voltage Controlled Resistor to balance the bridge. The electronic circuit has been designed in a standard integrated CMOS technology (AMS 0.35μm) with a low supply voltage (±1.5 V) and a reduced power consumption (lower than 4mW). PSpice simulation results show a very good agreement with theoretical expectations. The output voltage accuracy shows a 0.03V maximum absolute error for a range of ±50% of sensor variations from its baseline value. Very small baseline values are allowed (tens of μF).
Journal of Communications Software and Systems, 2018
In this work we present a combined 90/900 MHz Energy Harvesting Architecture for IoT device power... more In this work we present a combined 90/900 MHz Energy Harvesting Architecture for IoT device power assisting. The harvester takes advantages from a dedicated diplexer and a power manager for battery life enhancement purposes. The system has been optimized in the 900 MHz frequency range by analyzing a probabilistic approach used for modeling the possible amount of Global System for Mobile communication (GSM) energy that could be harvested while a fixed power downlink scenario has been adopted for the 90MHz band. A preliminary IC system with a 0.18μm CMOS SMIC technology has been designed and optimized at 90 and 900 MHz while discrete element board, to be integrated with the proposed IC, with commercial components has been developed and tested. Concerning simulation results on the IC design they have confirmed that the integrated system handles an incoming power typically ranging from-25 dBm to 5 dBm by rectifying the variable input signals into a DC voltage source with an average 50% efficiency. Keywords-Radio frequency energy harvesting, rectifiers, probabilistic modelling, dual band energy harvesting. I. INTRODUCTION Nowadays energy recovery from environmental power sources is an innovative and appealing way to capture and store energy for small, wireless and autonomous devices commonly used in wearable electronics, low voltage or low power circuit and systems, and, more and more, on Wireless Sensor Network (WSN) systems [1-5]. Energy Harvesting (EH) is the process of scavenging ambient energy from sources in the surrounding environment. It is an attractive method for overcoming the energy limitations of conventional battery powered wireless devices. As a consequence, efficient harvesters can potentially lead to significant reduction in the costs associated with replacing batteries periodically. The best-known EH collectors are large solar panels and wind generators, which have become major alternative energy
Journal of Communications Software and Systems, 2017
In this work we present an IC architecture for RF energy harvesting. The system has been designed... more In this work we present an IC architecture for RF energy harvesting. The system has been designed with a 0.18μm CMOS SMIC technology and optimized at 900MHz. Simulation results have confirmed that the integrated system handles an incoming power typically ranging from -25 dBm to 20 dBm by rectifying the variable input signals into a DC voltage source with an overall efficiency up to 50%. The chip area estimation for the proposed system is as low as 3x3mm2.
In this work, we present an innovative low cost sensor and algorithm for the monitoring and measu... more In this work, we present an innovative low cost sensor and algorithm for the monitoring and measurement of solar irradiance. This parameter is usually estimated using pyranometers, often based on thermopile. They are quite expensive, also because need additional hardware for data acquisition and manipulation as well as non-negligible installation costs. The system architecture and novel algorithm here proposed employ small PhotoVoltaic (PV) cells and a digital sensor interface. Moreover, the logic section permits to tilt the sensor allowing to track the sun with improved accuracy.
An integrated pulseoximeter/heartbeat rate detector is herewith described. The ready-to-use capab... more An integrated pulseoximeter/heartbeat rate detector is herewith described. The ready-to-use capability and its easy portability make the device a reliable, non-intrusive detector to be used in a large amount of applications (medical, domestic monitoring, sport scenarios). Both the blood oxygen percentage detection (i.e. pulsoximetry) and heartbeat rate monitoring are obtained thanks to a light-sensible set of diodes and receivers, by opportunely evaluating the emitted and received power light ratio through the body, using a standard technique. Test results have demonstrated that a simple 10-bit A/D converter can display both the O2 blood concentration percentage and the heartbeat rate accurately.
A new analog lock-in amplifier for automatic measurements of very small and noisy signals is prop... more A new analog lock-in amplifier for automatic measurements of very small and noisy signals is proposed here. The integrated system, which is particularly suitable for the accurate detection in sensor applications, performs continuously the relative phase alignment and the frequency tuning of input and reference signals through automatic operations ensured by suitable feedbacks. The complete structure of this amplifier has been implemented both as a PCB, with discrete commercial components, and as an ASIC, fabricated in AMS 0.35 μm standard CMOS technology. The system has been optimized to operate in the operating frequency range (2.5 ÷ 25) Hz, so resulting suitable for different sensor applications. Conducted measurements, also employing commercial resistive gas sensors for the ethylene glycol revelation, have demonstrated the system validity and its satisfactory performances in the detection of noisy signal amplitudes, also down to tens of nV. Moreover, with respect to a simpler resistive voltage divider, typically used as a basic sensor interface, the resolution improvement provided by the proposed lock-in allows a theoretical concentration detection in the order of tens of ppb.
A new oscillating circuit is proposed to estimate resistance and parallel parasitic capacitance o... more A new oscillating circuit is proposed to estimate resistance and parallel parasitic capacitance of chemical sensors. The circuit is able to reveal resistance in a wide range, from tens of k Omega to over than 100 G Omega. Experimental results of a discrete board prototype confirm the very good performance of post-layout simulation tests concerning the CMOS integrated implementation.
2009 Ph.D. Research in Microelectronics and Electronics, PRIME 2009, 2009
In this paper we present a novel internal architecture of low-voltage and low-power positive seco... more In this paper we present a novel internal architecture of low-voltage and low-power positive second-generation current conveyor (CCII+). The proposed internal circuit topology, designed in standard CMOS technology (AMS 0.35 ¿m), employs an n-type differential pair as input stage, while a cascoded push-pull configuration implements a very high impedance output stage. A degenerated nMOS common drain topology reduces X node impedance. The choice of internal CCII+ architecture, concerning both its stage architecture and transistor sizes, has been made in the direction of designing a quasi-ideal CCII+ in terms of parasitic components at its terminals. The developed CCII+ operates at low supply voltages of ±1 V with a total power consumption of about 300 ¿W, so it is suitable for general purpose portable applications. It has been also characterized implementing well-known applications, both in time and frequency domains, such as signal processing circuits and impedance simulators.
2007 IEEE International Symposium on Circuits and Systems, 2007
In this paper we describe an approach for the design of high-accuracy, high-precision, current mo... more In this paper we describe an approach for the design of high-accuracy, high-precision, current mode amplifiers. These circuits take advantage of dynamic element matching (DEM) for compensating the input offset and /f noise voltages of the nominally identical (source-coupled) transistor pairs in a second generation current conveyor (CCII). In comparison with high-accuracy, high-precision op amp based amplifiers, the proposed approach is more convenient if the gain of the op amp may not be very high, e.g. due to short channel effects.
Parallel arrays of well aligned crack-free N-doped and undoped TiO 2 nanofibers (3-4 mm long, 300... more Parallel arrays of well aligned crack-free N-doped and undoped TiO 2 nanofibers (3-4 mm long, 300-500 nm diameter) have been deposited by near field electrospinning (NFES) technique on Si 3 N 4 substrates with interdigitated Pt electrodes and annealed at 400 • C for 1 h. Anatase TiO 2 with crystallites' size of approximately 12 nm have been prepared and characterized by XRD, SEM, TEM and XPS techniques. Experimental measurements have been conducted through an ad hoc analog integrated resistive sensor interface, based on an oscillating circuit, fabricated in a 0.35 m standard CMOS technology. Gas response to NO 2 in the range 1-10 ppm and 100-300 • C operating temperature (OT) has shown best practical sensor sensitivity (S = R G /R A) at a relatively low OT (150 • C) and detection limits down to 1 ppm gas. Nitrogen doping at N:Ti 1:1 atomic ratio has been proposed in order to decrease the intrinsic resistance of TiO 2 , thus enabling better signal to noise ratio of the electrical response.
IEEE Transactions on Instrumentation and Measurement, 2010
The main issue concerning metal oxide (MOX) gas sensors is mostly related to the wide range of re... more The main issue concerning metal oxide (MOX) gas sensors is mostly related to the wide range of resistive values that the sensors can show. In addition, some sensors could have baseline resistive values up to tens of gigohms. To avoid the use of expensive picoammeters or the use of circuits adopting scaling factors, different solutions have recently been proposed, exploiting the resistance-to-time conversion (RTC) technique. They show good linearity and are suitable for the integration in a chip together with the elaboration unit, but they may require long measurement time (tens of seconds) if high resistance values need to be estimated. In addition, they may suffer the influence of a sensor parasitic capacitance, in parallel with the resistive component. In this paper, a new method is proposed to reduce the measuring time, keeping the advantages offered by the RTC approach and including a parasitic capacitance estimation feature. Particularly, an effective architecture, based on moving thresholds, has been proposed, simulated, and experimentally tested with commercial resistors (values between 1 MΩ and 100 GΩ) and capacitors (values between 1 and 47 pF). Finally, a fast sensor transient, due to a rapid change in the heating power, has been acquired with the proposed instrument and compared with a similar transient analyzed with a classical RTC approach. This test has shown the applicability of the interface for solutions requiring detailed information of the sensor response, such as the characterization of new sensors (e.g., nanowires) or the behavior analysis during nonstandard thermal profiles. Index Terms-Fast transient analysis, high resistive sensor, low measuring time, parasitic capacitance estimation, wide-range resistances. I. INTRODUCTION M ETAL oxide (MOX) gas sensors are often used due to their advantages, namely, good sensitivity to relevant gases, low production cost, and small size. They react to the presence of the gas by varying the conductivity; therefore, they can be considered as resistive sensors. In addition, due to the particular processes used to implement the sensor and to the Manuscript
IEEE Transactions on Circuits and Systems II: Express Briefs, 2008
In low-voltage, deep sub-m analog CMOS circuits, the accuracy and precision can be limited by the... more In low-voltage, deep sub-m analog CMOS circuits, the accuracy and precision can be limited by the finite gain as well as by the input offset and 1 noise voltages of opamps. Here, we show how to design high-accuracy high-precision CMOS amplifiers by properly applying dynamic element matching to a secondgeneration current conveyor (CCII); if all of the critical, nominally identical transistor pairs are dynamically matched, the resulting amplifier has low residual input offset and noise voltages. When compared with chopper or traditional dynamic element-matching amplifiers, the proposed approach alleviates the tradeoff between output swing and output resistance and is more robust against the finite opamp gain. Transistor-level simulations confirm theoretical results.
ABSTRACT Chemical sensors for gas detection nowadays are widely used in several applications; bas... more ABSTRACT Chemical sensors for gas detection nowadays are widely used in several applications; basically, electrochemical sensors and semiconductor devices are used for this purpose. In both cases, the sensor value estimation is usually implemented as a current measurement and they are often referred as current-output sensors. In this paper, a versatile and low-cost interface circuit for such kind of sensors is presented. The proposed solution is characterized by a wide measurement range, yielding flexibility of use with sensors showing different baseline values. In addition, the fast readout time, on the order of tens of milliseconds, guarantees an accurate acquisition of the sensor data even in presence of fast transients, for example when using sensors operated in pulsed thermal regimes. The front-end works with a single-voltage power supply and furnishes a time-coded digital output signal, thus it is suitable to be directly interfaced to a microcontroller for the management of the measurement process, data elaboration, and presentation. Simplicity and compactness of the electronic interface make possible the integration in a single-chip solution, together with the digital electronics. Reproducibility of the circuit, for applications requiring the simultaneous acquisition of multiple sensors, is furthermore facilitated. The proposed approach has been validated with experimental tests conducted on a discrete component prototype. The system characterization has shown a maximum linearity error in the estimation of the sensor current or resistance of ~ 5% over a measurement range of seven decades; the measurement time is in all the considered input range. Fast thermal transients of different semiconductor sensors for gas sensing have been successfully acquired, demonstrating the validity of the proposed approach. Power dissipation ( at 3.3 V) and the front-end cost ( ~ 10 $) make the presented solution suitable for the employment in low-cost and low-power gas detection system- .
In this paper, we propose a low-voltage (LV) low-power (LP) oscillating circuit suitable for the ... more In this paper, we propose a low-voltage (LV) low-power (LP) oscillating circuit suitable for the read-out of DC-excited resistive gas sensors, based on Second Generation Current Conveyors (CCIIs). This low-cost fully integrable front-end is able to evaluate the resistive behavior of gas sensors, without any preliminary calibration, operating a Resistance to Time ( R-T) conversion and exciting the sensor with
The use of capacitive sensors has advantages in different industrial applications due to their lo... more The use of capacitive sensors has advantages in different industrial applications due to their low cost and low-temperature dependence. In this sense, the current-mode approach by means of second-generation current conveyors (CCIIs) allows for improvements in key features, such as sensitivity and resolution. In this paper, a novel architecture of CCII for differential capacitive sensor interfaces is presented. The proposed topology shows a closed-loop configuration for both the voltage and the current buffer, thus leading to better interface impedances at terminals X and Z. Moreover, a low power consumption of 600 µW was obtained due to class-AB biasing of both buffers, and the inherent drawbacks in terms of linearity under the mismatch of class-AB buffering are overcome by its closed-loop configuration. The advantages of the novel architecture are demonstrated by circuit analysis and simulations; in particular, very good robustness under process, supply voltage and temperature vari...
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Papers by Giuseppe Ferri