Massimo Scarsella

This work presents 28 schemes of RC oscillators that make use of a single second-generation voltage conveyor (VCII). Since the active elements are the only source of biasing current, this schemes represent a valid solution when energy-efficient performances are required. The proposed circuits enjoy all the benefits of the current-mode approach. Moreover, employing a VCII, there is no need of an additional buffer for the voltage output readout, helping to keep system power consumption low. All the proposed configurations use only 3 resistors and 2 capacitors, that is a lower number of components with respect to operational amplifier (OA) RC oscillators. This also reduces the power dissipation on resistors due to Joule effect. A comprehensive theoretical analysis is provided to determine the theoretical oscillation condition (OC) and frequency, and the schemes are grouped based on this. Experimental tests using both simulations and measurements with the commercial AD844 as a VCII are performed to validate theory. In particular, among the 28 schemes, 16 proved to work as per theory developed considering an ideal VCII, and sample experimental measurements are reported for such schemes. On the other hand, the other 12 schemes are found to not work with the AD844 as a VCII due to its parasitic elements, but they proved to work when computer simulated with an ideal VCII confirming the correctness of the theoretical treatment. An application example as sensor interface is finally proposed.

Rockfalls and landslide events are caused by different factors among which are included geomorphological and climatic factors and also human interaction. Therefore, the economic and social impacts can be significant and the remote monitoring of such hazards has become an essential topic in various applications. Wireless sensor networks (WSNs) are well suited for the deployment of monitoring systems, benefiting from the different technologies and topologies that are available and evolving nowadays. This review paper aims to summarize and overview the up-to-date state of the art of rockfall and landslide monitoring systems based on WSNs. The implementation and methods were analyzed for each solution, along with the system architecture and relevant hardware aspects. All the retrieved data were used to analyze the current trends and future possibilities in the field of WSN geohazard monitoring.

In this study, a review of second-generation voltage conveyor (VCII) and current conveyor (CCII) circuits for the conditioning of bio signals and sensors is presented. The CCII is the most known current-mode active block, able to overcome some of the limitations of the classical operational amplifier, which provides an output current instead of a voltage. The VCII is nothing more than the dual of the CCII, and for this reason it enjoys almost all the properties of the CCII but also provides an easy-to-read voltage as an output signal. A broad set of solutions for relevant sensors and biosensors employed in biomedical applications is considered. This ranges from the widespread resistive and capacitive electrochemical biosensors now used in glucose and cholesterol meters and in oximetry to more specific sensors such as ISFETs, SiPMs, and ultrasonic sensors, which are finding increasing applications. This paper also discusses the main benefits of this current-mode approach over the classical voltage-mode approach in the realization of readout circuits that can be used as electronic interfaces for different types of biosensors, including higher circuit simplicity, better low-noise and/or high-speed performance, and lower signal distortion and power consumption.

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 V_C 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 well as non-ideal current and voltage gains of the used ABBs is presented. The proposed circuit is designed at the transistor level in 0.18 µm and ±0.9 V supply voltage. Simulation results using the SPICE program show a multiplication factor ranging from ±10 to ±25.4 with a maximum error of 0.56%. As an example, the application of the achieved floating capacitor as a standard high pass filter is also included.

The aim of this paper is to prove that, through a canonic approach, sinusoidal oscillators based on second-generation voltage conveyor (VCII) can be implemented. The investigation demonstrates the feasibility of the design results in a pair of new canonic oscillators based on negative type VCII (VCII⁻). Interestingly, the same analysis shows that no canonic oscillator configuration can be achieved using positive type VCII (VCII⁺), since a single VCII⁺ does not present the correct port conditions to implement such a device. From this analysis, it comes about that, for 5-node networks, the two presented oscillator configurations are the only possible ones and make use of two resistors, two capacitors and a single VCII⁻. Notably, the produced sinusoidal output signal is easily available through the low output impedance Z port of VCII, removing the need for additional voltage buffer for practical use, which is one of the main limitations of the current mode (CM) approach. The presented theory is substantiated by both LTSpice simulations and measurement results using the commercially available AD844 from Analog Devices, the latter being in a close agreement with the theory. Moreover, low values of THD are given for a wide frequency range.