Giuseppe Ferri

An electronic nose for food analysis

Since the first developments of electronic noses, food analysis has been considered as one of its most useful applications. In this paper an electronic nose based on quartz microbalances coated with metallo-porphyrins and related compounds is presented and illustrated. Extensive tests on various substances playing key roles in food analysis show that sensing properties of the sensing materials (in terms of sensitivity and selectivity) can be exploited for electronic nose applications devoted to the analysis of various kinds of foods. The versatility of this system has been successfully tested on different kinds of foods, such as fish, meat, vegetable and wine for which results are shown.

The application of metalloporphyrins as coating material for quartz microbalance-based chemical sensors

Abstract The results of both optimization and tests to prove the suitability of an array of quartz microbalance sensors (QMBs) modified with various metalloporphyrins for the determination of food freshness are presented and discussed. As far as optimization is concerned, it was found that a minimum amount of 50 μg of metalloporphyrin must be used for the modification of the quartz microbalance sensors in order to obtain the maximum sensitivity. The sensory behavior of five different porphyrins was subsequently studied. QMBs were modified using four different meso -tetraphenylporphyrins: phenyl, p -nitrophenyl, p -bromophenyl, p -methoxyphenyl and an octa-alkylporphyrin ( etio -porphyrin I), all loaded with a Co 2+ metal ion. A clear decrease in the sensitivity for the etio -porphyrin I was observed whereas for the meso -tetraphenyl-porphyrins the best response was obtained for the p -nitrophenyl derivative. These results can be attributed to the different electron densities which are present at the metal center of the macrocycle. The determination of the response behavior with respect to methanol, thiophene, diethylamine and triethylamine of a sensor array consisting of rhodium, ruthenium, cobalt, and manganese meso -tetraphenylporphyrin revealed that there is a clear difference in terms of the sensitivity and hence, the selectivity for the various QMBs. The rhodium and the cobalt-based QMBs were alike and demonstrated a preference for the gases with soft donating sites, i.e. thiophene and the amines. The QMBs based on ruthenium and manganese demonstrated distinctly different behavior. The ruthenium-based QMB demonstrated no clear preference for gases with either hard or soft donating sites, whereas the manganese-based QMB preferred gases with hard donating sites, i.e. methanol. These results led to the overall conclusion that this sensor array could be used for the analysis of complex gas mixtures, where the most prevalent gases fall under the categories of the amines, the alcohols and the sulphides.

Analog circuits and systems for voltage-mode and current-mode sensor interfacing applications

Introduction.- 1. Physical and Chemical Sensors.- 2. Resistive, Capacitive and Temperature Sensor Interfacing Overview.- 3. The Voltage-mode Approach in Sensor Interfaces Design.- 4. The Current-mode Approach in Sensor Interfaces Design.- 5. Detection of Small and Noisy Signals in Sensor Interfacing: The Analog Lock-in Amplifier.- A1. The Second Generation Current-Conveyor (CCII).- A2. Noise and Offset Compensation Techniques.

A CMOS Integrable Oscillator-Based Front End for High-Dynamic-Range Resistive Sensors

A new oscillating circuit is proposed to estimate the resistance and parallel parasitic capacitance of resistive chemical sensors. The circuit is able to reveal the resistance in a wide range (from tens of kiloohms to more than 100 GOmega) due to the adopted resistance-to-time technique. In addition, the parallel capacitance (up to 50 pF) can be estimated. The circuit, which does not need any initial calibration, is very simple and compact and is suitable to be integrated with a standard CMOS technology to obtain a low-cost and low-power device for a sensor array interface. Different kinds of post layout simulations concerning the CMOS integrated implementation have been conducted. Experimental results obtained using a discrete prototype board, both on passive components and on real sensors (metal-oxide sensors), have shown good linearity and reduced percentage error with respect to the theoretical expectations.

A CCII‐based wide frequency range square waveform generator

SUMMARY In this paper, we propose a novel current-mode solution suitable for the square waveform generation. The designed oscillator, which utilizes only two positive second-generation current conveyors as active blocks, six resistors and a capacitor, is based on a current differentiation, instead of voltage integration, typical of developed solutions both in voltage-mode and in current-mode approaches, so avoiding circuit limitations due to the node saturation effects. The proposed circuit has been designed, as an integrated solution at transistor level, in a standard CMOS technology, with low-voltage (± 1V) and low-power (430µW) characteristics. Simulation results have confirmed the good circuit behaviour, also for working temperature drifts, showing good linearity in a wide oscillation frequency range, which can be independently adjusted through either capacitive (in the range pF − µF) or resistive (in the range M Ω–G Ω) external passive components. Waiting for the chip fabrication, preliminary measurements have been performed using a laboratory breadboard employing the CCII with AD844 commercial component and sample capacitors and resistors. The experimental results have shown good agreement with both simulations and theoretical expectations. Copyright

High-valued passive element simulation using low-voltage low-power current conveyors for fully integrated applications

In this brief, we describe how, using low-voltage low-power second-generation current conveyors, it is possible to simulate the frequency behavior of high capacitances and inductances by utilizing only elements suitable for an integrated implementation. The effect of current conveyor nonidealities has been taken into account. The simulated inductances and capacitances have been utilized, as an example, in the design of a fully integrated bandpass filter. PSPICE simulations, performed employing a standard CMOS technology (ALCATEL Mietec 0.5 /spl mu/m) and showing good performance of the presented circuits, are also reported.

An ultralow-power switched opamp-based 10-B integrated ADC for implantable biomedical applications

This paper describes an ultralow-power switched opamp-based integrated analog-to-digital converter (ADC) for cardiac pacemakers applications. The ADC consumption, measured on 10 chip samples and averaged, is 8.18 /spl mu/W (stand-by value: 1 nW) for the analog part and of 9.71 /spl mu/W (5 nW) for the digital one, using a supply battery of 2.8 V. The converter has a resolution of 10-b, its typical operating clock frequency is 32 KHz (2.9 KS/s sampling rate) and is able to reach the same resolution at 2 V (0.7 KS/s sampling rate), with a dissipation of 1 /spl mu/W and 1.3 /spl mu/W for analog and digital part, respectively.

A Fully-Analog Lock-In Amplifier With Automatic Phase Alignment for Accurate Measurements of ppb Gas Concentrations

A novel fully-analog lock-in amplifier for the accurate measurements of low quantities of gas in sensor applications is here presented. When compared with commercial lock-in and other solutions available in the literature, the proposed system implements an automatic alignment of the relative phase between input and reference signals, both at power-on and for any variation of the input signal phase and amplitude during the working time, so allowing to detect, accurately and in a continuous way, the mean value of the input signal coming from sensors (typically buried into noise). The circuit has been optimized to operate at a specified reference frequency, in particular 77 Hz; this value is suitable for gas sensor applications, since it avoids also any kind of interferences at 50 Hz net frequency and its harmonics. Experimental results have confirmed the correct functionality of the system, also tested for both carbon monoxide (CO) and ethylene glycol detections. With respect to the simpler resistive gas sensor interface, implemented by a resistive voltage divider, the improvement experimentally given by the proposed automatic lock-in amplifier, in terms of resolution, has been of a factor of about 100 for the CO and 230 for the ethylene glycol measurements, so allowing a theoretical gas detection in the order of ppb.

A New and Fast-Readout Interface for Resistive Chemical Sensors

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 M¿ and 100 G¿) 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.

A CCII-Based Low-Voltage Low-Power Read-Out Circuit for DC-Excited Resistive Gas Sensors

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 a DC voltage. Through the use of CCIIs, all the Current-Mode (CM) benefits in LV LP integrated architecture design are achieved. The developed interface, designed at transistor level, is able to operate with a low supply voltage (plusmn0.75 V), showing a low power consumption of about 700 muW, and, hence, it is suitable for portable applications. Both CADENCE simulations on the designed integrated solution and experimental results, achieved using a PCB prototype, have shown a linear characteristic and a good agreement with theoretical expectations, for more than four decades of resistive variation. Experimental measurements, conducted employing low cost commercial components (AD844 as CCII and Figaro TGS 2600 device as resistive gas sensor), have confirmed the good performances of the developed read-out circuit as resistive gas sensor interface.