Published in IET Circuits, Devices & Systems Received on 2nd December 2009 Revised on 1st April 2010 doi: 10.1049/iet-cds.2009.0330 ISSN 1751-858X Grounded capacitor current mode single resistance-controlled oscillator using single modified current differencing transconductance amplifier D. Biolek 1 A.U ¨ . Keskin 2 V. Biolkova 3 1 Department of EE/Microelectronics, University of Defence/Brno University of Technology, Czech Republic 2 Department of Biomedical Engineering, Yeditepe University, Kayisdagi 34755, Istanbul, Turkey 3 Department of Radio Electronics, Brno University of Technology, Czech Republic E-mail: dalibor.biolek@unob.cz Abstract: This study proposes a current mode canonical single resistance-controlled oscillator (SRCO) circuit based on a single modified current differencing transconductance amplifier.The circuit employs grounded capacitors and provides a current output with high output impedance. The proposed circuit also enables orthogonal control of frequency and oscillation condition. The performance of the proposed SRCO is verified by means of simulation program with integrated circuit emphasis (SPICE) simulations, on-chip experiments and measurements. 1 Introduction Many single resistance-controlled oscillators (SRCOs) are available in literature [1–19]; however, only some of them operate in current mode (CM). References [7–15] are four- terminal floating nullor (FTFN)-based CM circuits. Aggarwal [16] presents a differential difference current conveyor (DDCC)-based oscillator with some floating passive components. Chang et al. [17] propose two CM circuits using grounded passive components and a fully differential current conveyor (FDCCII). The work in [18] presents a current mode SRCO using a single differential voltage current conveyor (DVCC) (they used the name DVCCC) and five passive components. However, oscillation frequency is varied through a floating resistor in their circuit. Another study [19] proposes eight CM single element controlled oscillator circuits, each of which consisting of five grounded passive components and two DVCCs. On the other hand, the current differencing transconductance amplifier (CDTA) [20] has found much interest in electronics community. The CDTA is a universal active building block for implementing many signal processing functions [21–27] including sinusoidal oscillators [28–34]. Recently, a single-CDTA-based SRCO circuit has been reported by Prasad et al. [35], which enables independent control of the frequency of oscillation (FO) and the condition of oscillation (CO). However, although it operates in the CM, this circuit does not provide an SRCO structure with all-grounded capacitors and high-impedance output terminals. Such feature is provided by a structure published in [36] but with two CDTAs. The author of [36] believes that ‘... any realisation of a CDTA oscillator employing all-grounded passive elements (AGPE) and providing independent control of CO and FO would make use of at least two CDTAs ...’ [36, p. 2]. The modified CDTA [37] used in this study is an extension of the conventional CDTA [20]. According to its schematic symbol in Fig. 1a, it has a pair of low-impedance current inputs p and n, and an auxiliary terminal z, whose outgoing current is the difference of input currents. In addition to the CDTA, a copy of the z-terminal current is also available at the zc high-impedance terminal. Therefore this modified CDTA element is called ZC-CDTA (Z Copy CDTA) [37]. Similar to the CDTA, this element provides a pair of x-terminals whose currents are equal in magnitude, but flow in opposite directions, and the product of transconductance ( g m ) and voltage at the z-terminal 496 IET Circuits Devices Syst., 2010, Vol. 4, Iss. 6, pp. 496–502 & The Institution of Engineering and Technology 2010 doi: 10.1049/iet-cds.2009.0330 www.ietdl.org