Realisation of Single-Resistance-Controlled Sinusoidal Oscillator: A new application of the CDTA DINESH PRASAD * , D.R.BHASKAR *1 and A.K.SINGH + * Department of Electronics and Communication Engineering, F/O Engineering and Technology, Jamia Millia Islamia, Jamia Nagar, New Delhi-110025, India + Department of Electronics and Communication Engineering, Inderprastha Engineering College, Shahibabad, Ghaziabad (UP), 201010, India *1 drbset@yahoo.com Abstract: - Among various modern active building blocks, the recently introduced ’current differencing transconductance amplifier’ (CDTA) is emerging as a very flexible and versatile building block for analog circuit design and has been used earlier for realizing a variety of functions. In this paper, a new application of the CDTA in realising a Single Resistance Controlled Sinusoidal Oscillator has been introduced. The proposed circuit employs only a single CDTA alongwith a bare minimum of only four passive components and yet offers the advantages of (i) independent control of condition of oscillation and frequency of oscillation and (ii) low active and passive sensitivities. The workability of the proposed configuration has been demonstrated by experimental results. Key-Words: - Current Differencing Transconductance Amplifier, Sinusoidal oscillator, Current-mode circuits. 1 Introduction Single Resistance Controlled sinusoidal oscillators (SRCOs) find numerous applications in communication, control systems, signal processing, instrumentation and measurement systems, see[1]- [3] and the references cited therein. SRCOs based upon different active building blocks are available in the literature, see [4]-[12] and the references cited therein. The advantages, applications and usefulness of recently introduced new active building block named current differencing transconductance amplifier (CDTA) are now being recognised in literature [13]-[16]. Recently, a current-mode quadrature oscillator using two CDTA and six passive elements has been introduced [16]. However, to the best knowledge and belief of the authors, no SRCO using single CDTA has yet been presented in the open literature so far. The purpose of this paper is, therefore, to propose a new SRCO using a single CDTA along with a minimum possible number of passive components, which offers (i) independent control of oscillation frequency and condition of oscillation, and (ii) low active and passive sensitivities. SRCOs realizable with minimum components have the following advantages (i) minimum power dissipation, (ii) reduced likelihood of the circuit failure and (iii) reduced component cost, noise and parasitic effects [7]. The practicability of the new circuit has been demonstrated by experimental results based upon commercially available AD844 type CFOAs and LM3080 type OTAs. 2 New Oscillator Configuration The proposed new configuration is shown in Fig.1. Assuming an ideal CDTA characterised by V p =V n =0, I z =I p -I n , I x+ =g m V z , I x- =-g m V z , where V z = I z .Z z and Z z is the external impedance connected to the z-terminal of the CDTA [13]-[16]. C 1 R 1 p n z x - x + CDTA R 2 C 2 Fig.1: The proposed configuration. A routine circuit analysis yields the following characteristic equation: { } 0 2 2 ) ( 2 1 2 1 2 1 2 1 2 = + - + + G G g C G C C s C C s m (1) where 1 1 1 R G = and 2 2 1 R G = . Thus, the condition of oscillation (CO) and frequency of oscillation (FO) are given by: WSEAS TRANSACTIONS on ELECTRONICS Dinesh Prasad, D. R. Bhaskar, A. K. Singh ISSN: 1109-9445 257 Issue 6, Volume 5, June 2008