Vincenzo Stornelli

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

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.

A CCII-BASED HIGH IMPEDANCE INPUT STAGE FOR BIOMEDICAL APPLICATIONS

An integrated current mode high impedance input stage designed for Electrocardiography (ECG) systems (or low frequency general applications) is presented. This feature becomes necessary when a two-electrodes ECG apparatus is used (e.g., in fetal ECG or heart monitoring in extreme sports) and a good response of the system to common mode signals is required. The proposed input stage, based on a bootstrap topology that simultaneously increases the ECG electrodes input impedance (from 5 ÷ 50 kΩ to about 50 MΩ) and amplifies the applied signal, is implemented by using a configuration that employs only two second generation current conveyors for each electrode. Post-layout simulations have proved that the proposed system is quite not sensible to electrodes mismatch and battery discharge.

LOW VOLTAGE LOW POWER FULLY DIFFERENTIAL BUFFER

In this paper a useful CMOS fully-differential buffer topology is presented. The proposed solution, performing the common mode feedback operation, shows a rail-to-rail characteristic, so it is particularly suitable for low-voltage (± 0.75 V) low-power (< 400 μW) applications. The simulated results have shown excellent general performance, evaluated in terms of suitable figures of merit.

A Tuneable Active Inductor With High Dynamic Range for Band-Pass Filter Applications

An approach for the design of high-Q active inductor (AI) with high dynamic range is presented. The proposed AI includes a passive variable phase- and amplitude-compensating network and a highly linear inverting amplifier, forming a gyrator-C architecture. The equivalent inductance and resistance values are tunable in a wide frequency range; outside the operating frequency band, the inductor equivalent resistance increases, improving signal rejection for band-pass filter applications. As a feasibility demonstration, a first-order active band-pass filter using the high-Q active inductance has been fabricated and tested. The filter has a center frequency of 600 MHz and a measured noise figure of 11 dB with a 5-dBm 1-dB compression point and an 82-dB dynamic range.

Current-Mode High-Accuracy High-Precision CMOS Amplifiers

In low-voltage, deep sub- mum analog CMOS circuits, the accuracy and precision can be limited by the finite gain as well as by the input offset and 1/f noise voltages of opamps. Here, we show how to design high-accuracy high-precision CMOS amplifiers by properly applying dynamic element matching to a second-generation 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.

Low voltage integrated astable multivibrator based on a single CCII

In this paper we present a new low voltage (1.5V supply) astable multivibrator, implemented with a single CCII , that performs a controlled square wave generation. Complete theory calculations are addressed. Simulation results, obtained by means of Cadence simulator, are in a good agreement with theoretical expectations. Since the CCII has been implemented at transistor level, in a standard CMOS technology, the proposed multivibrator can be completely integrated. The maximum oscillation frequency obtained from simulations is about 50 MHz.

A novel low-voltage low-power fully differential voltage and current gained CCII for floating impedance simulations

In this paper we present a new current-mode basic building block that we named voltage and current gained second generation current conveyor (VCG-CCII). The proposed active block allows to control and tune both the CCII current gain and the voltage gain through external control voltages. It has been designed, at transistor level in a standard CMOS technology (AMS 0.35@mm), with a low single supply voltage (2V), as a fully differential active block. The proposed integrated solution, having both low-voltage (LV) and low-power (LP) characteristics, can be applied with success in suitable IC applications such as floating capacitance multipliers and floating inductance simulators, utilizing a minimum number of active components (one and two, respectively). Simulation results, related to floating impedance simulators, are in good agreement with the theoretical expectations.