Andrea De Marcellis

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 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 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.

Integration of GMR Sensors with Different Technologies

Less than thirty years after the giant magnetoresistance (GMR) effect was described, GMR sensors are the preferred choice in many applications demanding the measurement of low magnetic fields in small volumes. This rapid deployment from theoretical basis to market and state-of-the-art applications can be explained by the combination of excellent inherent properties with the feasibility of fabrication, allowing the real integration with many other standard technologies. In this paper, we present a review focusing on how this capability of integration has allowed the improvement of the inherent capabilities and, therefore, the range of application of GMR sensors. After briefly describing the phenomenological basis, we deal on the benefits of low temperature deposition techniques regarding the integration of GMR sensors with flexible (plastic) substrates and pre-processed CMOS chips. In this way, the limit of detection can be improved by means of bettering the sensitivity or reducing the noise. We also report on novel fields of application of GMR sensors by the recapitulation of a number of cases of success of their integration with different heterogeneous complementary elements. We finally describe three fully functional systems, two of them in the bio-technology world, as the proof of how the integrability has been instrumental in the meteoric development of GMR sensors and their applications.

Fast, Versatile, and Low-Cost Interface Circuit for Electrochemical and Resistive Gas Sensor

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

A Novel Analog Autocalibrating Phase-Voltage Converter for Signal Phase-Shifting Detection

) make the presented solution suitable for the employment in low-cost and low-power gas detection systems.

A complementary metal oxide semiconductor—integrable conditioning circuit for resistive chemical sensor management

In this study, we present a novel analog read-out circuit, operating a phase-voltage conversion, suitable for the detection of signal phase shifting for micro- and nano-sensor system applications. Its main characteristics are the following: good linearity in the considered phase-shift range, capability of phase sign detection, independence from input signal amplitudes, setting and zeroing of the offset, autocalibration, high sensitivity and resolution, and high accuracy and precision. For these reasons and, in particular, thanks to its simple internal topology, the developed circuit can be considered as a suitable analog interface for portable measurement systems. Experimental results, achieved through a laboratory breadboard and using sample signals, have confirmed, with respect to the other solutions reported in literature, better linearity, higher sensitivity (equal to about 37 mV/degree in the ±90° phase-shift range) and resolution (lower than 0.1° in the same phase-shift range) for both positive and negative phase variations. When a more reduced phase-shift range must be detected (i.e., for optical sensor applications), it is possible to set the circuit parameters to further increase sensitivity and resolution.

Novel Modified De-Sauty Autobalancing Bridge-Based Analog Interfaces for Wide-Range Capacitive Sensor Applications

This paper presents a new interface circuit (for MOX-based resistive chemical sensors) capable of overcoming the main limit of the circuits based on the resistance-to-time approach, i.e. the long measuring time with high-value resistances. The system is designed to operate with a single supply of 3.3 V, thus facilitating an ASIC implementation together with digital electronics for a first data analysis and transmission. This is particularly advantageous when the elaboration process requires a large computational load and a data pre-elaboration is advisable. Simulations of the integrable solution of the system have shown the feasibility of the proposed approach. A prototype with discrete components has been furthermore fabricated and experimentally tested, showing good performance in the range 0.5 MΩ to 10 GΩ with a maximum measuring time of 60 ms.

One-Decade Frequency Range, In-Phase Auto-Aligned 1.8 V 2 mW Fully Analog CMOS Integrated Lock-In Amplifier for Small/Noisy Signal Detection

In this paper, we propose novel fully analog uncalibrated readout circuits for wide-range capacitance estimation. The working principle is based on a modified De-Sauty ac bridge configuration where two capacitances and two resistances are employed. Through the use of a voltage controlled resistor and of a suitable feedback loop, an accurate estimation over a wide range of the sensor capacitance variation is possible, also without the knowledge of the other bridge component values. The first two proposed solutions are able to estimate, experimentally, ~1.5 decades (optimized range: [25-840 nF]) and more than 3 decades [900 pF-1.1 μF] of capacitive variations, respectively, ensuring, continuously, the bridge equilibrium condition; the third interface allows the evaluation of the sensor capacitance also outside this condition, increasing the capacitive variation decades to more than 4 [81 pF-1.1 μF]. The proposed topologies have been also modified to detect the capacitive sensor parasitic resistance. In this case, experimental results on PCB have demonstrated the capability to simultaneously estimate ~ 1.7 capacitive [2-100 nF] and 1.5 resistive variation decades [33 kΩ-1.2 MΩ]. Finally, a suitable optimization of the operating range of the first proposed solution, obtained through a proper passive components sizing, has been performed with the aim to employ the commercial humidity sensor HCH-1000 in a high accuracy (11.4 bits) RH% detection.

A CCII‐based non‐inverting Schmitt trigger and its application as astable multivibrator for capacitive sensor interfacing

In this paper, we present a new fully analog integrated lock-in amplifier (LIA) for the accurate detection and the measurement of small, slow, and noisy signals, typical of sensors. The proposed LIA, designed as an integrated circuit in a 0.35