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OTA Based Floating Inductance Simulator Lalit Soni Priyanka Soni NTPC, Deesikha, Kaniha, Angul Orissa, India [email protected],[email protected] Marudhar Engineering College, Raisar Bikaner, Rajasthan, India [email protected] Abstract— A design of OTA based low pass filter is introduced in this paper. The circuit implementation is based on the floating inductor, floating resistor and grounded resistor which uses CMOS based operational transconductance amplifier (OTAs) as an active element. This filter is synthesized from low-pass LC prototype and designed using ladder structure. The simulation has been carried out on Tanner EDA tool 13.0 on 0.5µm technology. Keywords— Floating inductor, grounded inductor, OTA, Inductance simulator, low-pass LC prototype, low pass filter I. we propose the 3-OTA based floating inductor. The experimental results are shown in section IV and we draw the conclusions in Section V. II. OPERATIONAL TRANSCONDUCTANCE AMPLIFIER In the ideal OTA, the output current is a linear function of the differential input voltage, calculated as follows Iout = (Vin+ − Vin− )g m (1) The transconductance gain (gm) of OTA can be expressed as INTRODUCTION g m = √2βIB The performance of filters designed by the use of passive components degrades at audio frequencies and the required resistances and inductances values calculated from the mathematical expression are very difficult to meet from the market. Filters are indispensable parts of any communication systems. There are various topologies to design a filter depending upon the specifications and the application in which the filter has to be employed like for low frequency applications, active implementation is the best suited. Keeping in view these applications, the filter has been designed by replacing all the passive components in a passive network with an active device. OTA has been selected [1] as it suits us best for the purpose and its CMOS implementation is described. Electronically tuneable circuits attracted considerable attention in the design of analog integrated circuits because different values of resistance, inductance or capacitance can be obtained by the same device. The OTA provides a highly linear electronic tunability for a wide range and powerful ability to generate various circuits. Active inductors are preferable over their passive counterpart as the spiral wound passive inductor is bulky, expensive and incapable of operating at the moderate frequency range (KHz) without offering any signal loss. The recent trends are to use the OTA for realizing the floating inductor design [2] to use in place of the passive ones. OTA can be used as the basic active element for realizing the active inductors of both topologies; grounded and floating [3]. In this paper, a low pass filter has been taken up. This paper is organized as follows. In Section II, we presents basic operational transconductance amplifier. In section III, (2) Fig.1 Schematic of simple OTA The CMOS implementation of the simple OTA is used [4]. Note that β denotes the current factor [5]. It can be seen that β can be given by μn Cox (W⁄L)n and μp Cox (W⁄L)p for the NMOS differential pair based OTA and the corresponding PMOS respectively. Where µ is the mobility of the carrier, Cox is the gate oxide capacitance per unit area, W is the effective channel width, L is the effective channel length. From Eq. (2), the gm is proportional to (IB)1/2. III. CIRCUIT DESCRIPTION The conventional 3-OTA based inductor [3] is shown in Fig. 2. This circuit was implemented using OTA CA3280 which was constructed on transistor level. The proposed 3-OTA based inductor is shown in the Fig. 3. Fig. 4 RLC low pass filter topology Fig. 2 Conventional 3-OTA based floating inductor Fig. 5 Third-order low pass filter topology Fig. 6 Fifth-order low pass filter topology Fig. 3 Proposed 3-OTA based floating inductor and L2(only for fifth order) is of the value 1.66mH with IB=5 µA. We infer that the inductance can be electronically tuned by varying the external bias current IB. IV. EXPERIMENTAL RESULTS L12 = C gm 2 (3) To demonstrate the electronically tunable properties of the inductor, RLC low pass filter has been implemented . A third-order and fifth order low pass filter has been designed in this paper. An LC ladder topology has been adopted, in which R1 and R2 are OTA based floating and grounded resistor [6] respectively while L1 and L2(only for fifth order) are an active inductor. The capacitances C1,C2 and C3(only for fifth order) are set to 1pF. The source resistance R1=1/gm1 is chosen to be 1KΩ with IB =8.33mA and load resistance R2= 1/gm2 is chosen to be 28.86 KΩ with IB=10 µA. The simulated inductor L1 and L2(only for fifth order) is of the value 0.83mH with IB=10 µA and the simulated inductor L1 Fig. 7(a) Response of third order RLC low pass filter for L=0.83mH The proposed floating inductor and active low pass filter was simulated using TSPICE. The circuit was realized by CMOS implementation using 0.5 µm technology process parameters. The power supplies are selected as VDD = -VSS = 2.5V. Fig. 7(a), 7(b), 8(a) and 8(b) shows the plots of frequency response of RLC low pass filter. It can be seen that the proposed floating inductor can be employed instead of conventional if we are using CMOS technology. In this work, all the three OTAs for realizing the floating inductor are assumed to be identical for resulting in the equality of their corresponding parameters V. CONCLUSION Fig. 7(b) Response of third order RLC low pass filter for L=1.66 mH A floating inductor using 3-OTAs with one grounded capacitor has been proposed in this paper. The work has been focused on 0.5 µm CMOS technology. The inductance can be adjusted with external bias current of OTAs. The proposed circuit has been found to provide a sufficient accuracy and also promisingly applicable to the RLC low pass filter. Simulation results are showing the basic performance of the floating inductor. . REFERENCES [1]. [2]. [3]. [4]. [5]. [6]. Fig. 8(a) Response of fifth order RLC low pass filter for L=0.83mH Fig. 8(b) Response of fifth order RLC low pass filter for L=1.66 mH R.L. Geiger and E. Sanchez-Sinencio, "Active Filter Design Using Operational Transconductance Amplifiers: A Tutorial," IEEE Circuits and Devices Magazines, vol. 1, pp. 20-32, Aug. 1985. Petchmaneelumka W, “Simple floating inductance simulators using OTAs”, IEEE I2MTC '09., pp 10181021, May 2009. Koomagaew C, Petchmaneelumka W, Riewruja V, “OTA based Floating Inductance Simulator”, ICCAS-SICE, pp 857-860, Aug.. 2009. Kumngem M, Somdunyakanok M, Prommee P, “HighInput Impedance Voltage-Mode Multifunction Filter with Three-Input Single-Output Based on Simple CMOS OTAs” , ISCIT, pp 426-431, 2008. P.R. Kinget, "Device Mismatch and Tradeoffs in the Design of Analog Circuits", "IEEE Journal of Solid State Circuits," vol. 40, no. 6, IEEE, pp. 1212-1224, 2005. Franco Maloberti, “Analog Design for CMOS VLSI Systems”, Kluwer Academic pub 2001.