**1. Introduction**

There has always been an interest in designing sinusoidal oscillators due to several applications in different areas such as communication, instrumentation, biomedical, etc. [1–3]. Compared to LC and RLC sinusoidal oscillators, RC-active type oscillators are advantageous from the integration point of view. In the early implementations of RC-active sinusoidal oscillators, operational amplifiers (Op-Amps) were used as active elements [4–6]. A systematic approach was introduced in [5] to design Op-Amp-based oscillators with a single active element and the minimum number of passive elements. The design method of [5] resulted in Op-Amp-based oscillator configurations composed of one active device, two capacitors and four resistors.

However, the limited frequency performance and slew rate of Op-Amps as well as their high power consumption imposed a restriction in the application of Op-Ampbased sinusoidal oscillators. A literature survey shows that, after revealing the potential capabilities of current-mode (CM) signal processing, efforts have been made to design RC-active sinusoidal oscillators using various CM active building blocks (ABBs) [7–34]. Undoubtedly, second-generation current conveyor (CCII) as the main ABB of CM signal processing is the most widely used one for this purpose. Different approaches were employed to realize CCII-based oscillators. For example, in [8], the Op-Amps were replaced with composite current conveyors, resulting in CM oscillators. Unfortunately, this approach did not reach a simple realization because each amplifier could only be implemented with at least two CCIIs and two resistors. The extension of the approach presented in [5] was

**Citation:** Stornelli, V.; Barile, G.; Pantoli, L.; Scarsella, M.; Ferri, G.; Centurelli, F.; Tommasino, P.; Trifiletti, A. A New VCII Application: Sinusoidal Oscillators. *J. Low Power Electron. Appl.* **2021**, *11*, 30. https:// doi.org/10.3390/jlpea11030030

Academic Editor: Orazio Aiello

Received: 15 June 2021 Accepted: 6 July 2021 Published: 8 July 2021

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employed in [9] to synthesize CCII-based oscillators. Although the resulting sinusoidal oscillators enjoyed a canonic structure with the minimum possible number of elements, they were still not readily cascadable, i.e., they required additional voltage buffers to be actually usable in a real-world application. Most of the other CM oscillator realizations reported in [10–34] using different ABBs instead of CCIIs also suffered from a large number of active and/or passive elements.

Recently, the dual circuit of CCII, called second-generation voltage conveyor (VCII), has attracted the attention of researchers [35–44]. In particular, the recent study reported in [35,36] showed that this device helps to benefit from CM signal processing features and overcome the limitations in CCII-based circuits. Particularly, unlike CCII, there is a low-impedance voltage output port in VCII which allows it to be easily cascaded with other high-impedance processing blocks, without the need for extra voltage buffers in voltage output applications. Compared to CCII, VCII has proven superior performance in many applications [37]; up to now, this device has not been employed in the realization of sinusoidal oscillators.

However, the VCII, combining the advantages of CM processing with a voltage-mode interfacing, could provide sinusoidal oscillators operating up to higher frequency than Op-Amp-based ones. Moreover, breaking the gain-bandwidth tradeoff, it could ease decoupling oscillation frequency and oscillation condition even at the higher end of the spectrum. Among the possible implementations of VCII-based sinusoidal oscillators, those requiring the minimum number of (active and) passive components, so-called canonic, are of particular interest to minimize silicon area and power consumption. The aim of this work is only to present possible VCII-based canonic sinusoidal oscillator realizations, replicating the general approach presented in [5,9] which, as previously anticipated, has been used to synthesize Op-Amp-based and CCII-based sinusoidal oscillators. We will show that it is possible to implement sinusoidal oscillators with a minimum number of elements using a single negative type VCII (VCII−), two resistors and two capacitors, so demonstrating a new practical application of the VCII. The notable advantage of the proposed VCII−-based oscillator is that it is easily cascadable from port Z of VCII−, alleviating the need for any extra voltage buffer. Moreover, THD values are low also for higher frequency oscillators. However, the results of this study show that the applied approach does not reach any canonic configuration using positive type VCII (VCII+). The effect of non-idealities in the VCII has been considered, and the proposed approach has been tested by both simulations and measurement results.

The organization of this paper is the following: in Section 2, an introduction on the VCII as active building block as well as the basics of the general configuration of the VCII-based oscillator is introduced. Section 3 proposes, in detail, the study on the possible realizations of VCII-based oscillators, and the effects of non-idealities in VCII are considered in Section 4. Simulations and measurement results are given in Section 5. Finally, Section 6 concludes the paper.
