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Timestamp: 2019-04-22 04:24:53+00:00

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The current-mode approach is characterized by signals typically processed in the current domain. Current-mode circuits have some recognized advantages: firstly, they do not require a high voltage gain, so high performance amplifiers are not needed; secondly, they do not need high precision passive components, so they can be designed almost entirely with transistors; thirdly, current-input current-output operations can be easily performed, but their main advantage is in the overcoming the GBW limitation, typical of operational amplifiers. Second generation current-conveyor (CCII) is the basic current-mode analog block as well as the operational amplifier is that of voltage-mode analog design. CCII-based configurations can implement the basic analog functions having not only the voltage but also the current as input/output signals. CCII is characterized by a very simple internal topology, at transistor level. In an ideal CCII, if a voltage is applied at Y input node, an equal voltage is produced at X node, while the current flowing into X node is equal (CCII+) or opposite (CCII-) to the current flowing into Z node. Moreover, Y and Z nodes show ideal infinite impedances whereas X terminal shows zero impedance. Unfortunately, real CCIIs suffer from non-ideal parasitic impedances at their terminals. In our research activity, we have designed, in a standard CMOS technology, CCIIs both at transistor level (with improved performances in terms of parasitic impedances, obtained through suitable analog microelectronic techniques) and in novel or more efficient applications. In particular, recently our studies have regarded: the design of a CCII-based oscillator with reduced parasitic impedances ; the application of current-mode circuits to sensor interfaces [2-4]; the use of CCIIs in biomedical applications, in particular in electrocardiography and electroencephalography [5,6].
1) A. De Marcellis, C. Di Carlo, G. Ferri, V. Stornelli: “A CCII-based wide frequency range square waveform generator”, International Journal of Circuit Theory and Applications (march 2011).
2) A. De Marcellis, G. Ferri, P. Mantenuto, F. Valente, C. Cantalini, L. Giancaterini: “CCII-Based Interface for Capacitive/Resistive Sensors”, Proc. IEEE Sensors 2011, Limerick, Ottobre 2011.
3) A. De Marcellis, C. Di Carlo, G. Ferri, C. Cantalini, L. Giancaterini: “A CCII-based oscillating circuit as resistive/capacitive humidity sensor interface”, Atti del XVI Congresso AISEM (Associazione Italiana Sensori e Microsistemi) – Roma, Febbraio 2011, pp.293-299.
4) A. De Marcellis, G. Ferri, P. Mantenuto, C. Cantalini, L. Giancaterini: “Current-mode interface for gas/humidity sensors”, Atti della Riunione Gruppo Elettronica GE 2011, Trani, 6-8 Luglio 2011, ISBN 978-88-95612-85-0, pp.55-56.
5) V. Stornelli, G. Ferri: “A Single Current Conveyor-based Low Voltage Low Power Bootstrap Circuit for ElectroCardioGraphy and ElectroEncephaloGraphy Acquisition Systems”, Submitted to AICSP.
6) G. Ferri, V. Stornelli, A. Di Simone: “A CCII-based high impedance input stage for biomedical applications”, Journal of Circuits, Systems, and Computers, Vol. 20, No. 8 (2011) 1441-1447, DOI: 10.1142/S021812661100802X.
Integrated circuits supplied by low voltage and with reduced power consumption are widely used in sensors, microsystems and mixed A/D electronics, especially in the direction of combining, on the same chip, standard IC technology, sensing elements and processing electronics to implement smart sensors. In this sense, CMOS has been proved to be the main sensor technology, because it matches the reduction of costs and the simplicity of designing low voltage low power interfaces. The research group experience in this area has brought to the publication of an international research book edited by Springer on analog circuits and systems for voltage-mode and current-mode sensor interfaces . More in particular, in this field of research, we have developed, partially in collaboration with the University of Brescia, novel CMOS fully-integrable interfaces, for small and wide-range resistive/capacitive sensors, both with voltage-mode and current-mode approaches, for humidity and gas sensor applications. These circuits, if referred to resistive sensors, typically do not need any initial calibration, are able to reveal several decades of resistance variation and, at the same time, if necessary, also to estimate the sensor parasitic capacitance, showing high linearity and reduced percentage error between measured and theoretical calculations [2-4]. In this sense, recently we have also implemented different analog interfaces able to overcome the main limit of the circuits based on the resistance-to-time (RTC) approach, that is the variable and long measuring time that occurs when high-value resistances have to be evaluated [5-6].
In addition, we have developed, in collaboration with the University of Roma Tor Vergata, a novel fully-analog lock-in amplifier with automatic phase alignment for the accurate measurements of very low gas concentrations, that allows the self-alignment of the relative phase, both at power-on and for a variation of the input noisy signal phase during the working time, for the detection, in a continuous way, of the input signal (buried into noise) mean value [7-8]. This architecture has been designed and fabricated for thermally modulated sensors, working at low frequencies (717 Hz), where the signal coming from sensor has a small amplitude and is buried into noise. The designed lock-in amplifier guarantees the signal recovery from noise and has been proved to detect voltage levels as low as 100nV, corresponding to reagent substance lower than 1ppm. Recently, we have designed the integrated version, in CMOS technology, of this lock-in amplifier.
Always in this research field, we have developed a novel analog circuit that reveals the relative phase variation between input and reference signals having the same frequency and converts it into a DC voltage signal . The generated voltage level is independent from the signal amplitude variation and mean value, making the circuit suitable for any kind of input signal and waveform. The designed read-out circuit does not need any manual initial setting and/or operation because is capable to implement a phase detection loop for a complete automatic procedure of the measurement system. Moreover, it is possible to set sensitivity and resolution, depending on the phase shift to be revealed, and to null the output voltage for zero input phase difference.
Finally, a novel interesting modification of the Wheatstone bridge based interface has been recently proposed. It is a simple uncalibrated analog interface for the automatic and continuous estimation of wide-range resistance variations of a sensor whose baseline is unknown. The proposed circuit topology employs suitable feedback blocks providing the bridge balancing condition through the substitution of one of the bridge resistors by means of a voltage controlled resistor capable to compensate sensor variations. The sensor resistance is estimated for about five decades variation with a very reduced error [10-14].
1) A. De Marcellis, G. Ferri, Analog Circuits and Systems for Voltage-Mode and Current-Mode Sensor Interfacing Applications”, Springer, 2011.
2) A. Depari, A. Flammini, A. De Marcellis, G. Ferri: “A complementary metal oxide semiconductor-integrable conditioning circuit for resistive chemical sensor management”, IOP Measurement Science and Technology, 2011, Vol. 22, N. 12, dicembre 2011, pp. 1-7, DOI: 10.1088/0957-0233/22/12/124001.
3) A. De Marcellis, G. Ferri, A. Depari, A. Flammini: ”A Novel Time-Controlled Interface Circuit for Resistive Sensors”, Proc. IEEE Sensors 2011, Limerick, Oct. 2011.
4) A. De Marcellis, G. Ferri, C. Di Natale, E. Martinelli, A. D’Amico: “An analog automatic lock-in amplifier for accurate detection of very low gas concentrations”, Atti del XVI Congresso AISEM (Associazione Italiana Sensori e Microsistemi) – Roma, Feb. 2011, pp.285-291.
6) A. De Marcellis, G. Ferri, P. Mantenuto: “Automatic nulling Wheatstone bridge based resistive sensor interface”, Atti della Riunione Gruppo Elettronica GE 2011, Trani, 6-8 July 2011, ISBN 978-88-95612-85-0, pp.57-58.
Analog integrated circuit design has recently gone towards the direction of low-voltage low-power architecture working in battery-operated portable equipments, communications, sensors, hearing heads, etc.. This is also due to the development of smaller devices with lower threshold and breakdown voltages, to the increasing integration capability of VLSI technology as well as to the diffusion of the battery-operated systems for computer and telecommunication products, which requires the reduction of device weight and size and the increasing of their operative life. In this area, we have developed, in the last years, a number of integrated circuits for portable applications. Actually, this research has found new applications in energy harvesting and biomedicals.
A recent activity concerns the design of very high impedance input stages for two-electrodes electrocardiogram (ECG) recording systems. Standard ECG typically utilize three electrodes connected to an ECG amplifier, two of which (the sensing electrodes) attached on the thorax and the third, placed on a leg, being the reference electrode. The latter is typically connected to a Common Mode Feedback Block (CMFB) circuit, both reducing the common signals and ensuring the ground connection (for safety reasons). The use of two electrodes ECG systems (useful, for example, for fetal analysis or portable Holter monitors) needs the control of physical mismatch of electrodes that cannot be performed by typical CMFBs. For this reason, a suitable high impedance input stage has been designed, based on bootstrap topology, firstly in voltage-mode approach, recently with CCIIs [1-2].
Finally, in this area, a balanced antenna RF harvesting system, showing the miniaturization of the antenna/rectifier structure, has been also designed .
1) G. Ferri, V. Stornelli, A. Di Simone: “A CCII-based high impedance input stage for biomedical applications”, Journal of Circuits, Systems, and Computers, Vol. 20, No. 8 (2011) 1441-1447, DOI: 10.1142/S021812661100802X.
nonlinear conditions, or the synthesis of bifurcations if required. This method has been tested on practical circuits, and correctly detects instabilities.
Results are very promising, and a comparison and integration with other methods at international level has been carried out.
1) G. Leuzzi, V. Stornelli, “SB-PE Drift-Diffusion Algorithm For FET Devices Global Modeling”, Microelectronics Journal, 2011.
2) L. Pantoli, G. Leuzzi, A. Santarelli, F. Filicori, R. Giofrè, "Stabilisation Approach for Multi-device Parallel Power Amplifiers under Large-signal Regime", Proceedings of EuMW2011 (European Microwave Conference), Manchester, 2011.
Narrowband RF filters are the most difficult component to be integrated in an RF circuit. This is a serious disadvantage, because they appear in several locations in RF front-ends. For example, new radio architectures, such as direct conversion receivers, can reduce the number of RF filters in the receiver chain, but they cannot be eliminated. Moreover, the high-quality passive filters are the most expensive and bulky individual components in the RF section and they are cumbersome in automated manufacturing processes. One of the most serious limitations to active filters is their limited dynamic range, due to the low linearity of the proposed circuit solutions. Our approach yields a very wide dynamic range, by making use of very linear active devices, and tunable passive circuitry for tuning of the inductance value, of the losses, and of the frequency band. Tunability allows for flexibility in applications, and for compensation of temperature or fabrication tolerances. A one-transistor active inductor and a varactor constitutes the basic cell; two- and three-cell passband filters yield very high performances in terms of narrowband filtering, together with tunability. Low-power consumption versions are currently designed for implementation in SiGe monolithic circuits. Currently, measurements in thermal chamber are carried out, and also prototyping at professional level for field testing. A low-noise version, including noise compensation, has recently been patented, for use in front-end receiving circuitry and for VCO applications.
This activity is part of a PRIN research proposal together with other partner Universities, with the title: 'High-Performance Electronics in Flexible RF and Microwave Front-End Systems for Homeland Security and Remote Sensing Applications'.
1) G. Leuzzi, V. Stornelli, S. Del Re, L. Pantoli, “High quality factor integrable bandpass filter by using tunable active inductor”, INMMIC 2011, Vienna.
2) V. Stornelli, G. Leuzzi, L. Pantoli, S. Del Re, “High Dynamic Range Bandpass Filters Design Based on Active Inductor”, EuMiC 2011, Manchester.
3) G. Leuzzi, V. Stornelli, S. Del Re, “Tuneable Active Inductor with High Dynamic Range for Bandpass Filter Applications”, IEEE Transactions on Circuits and Systems II, vol.58, pp.647-651, 2011.

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