Circuits and Systems, 2013, 4, 29-33 http://dx.doi.org/10.4236/cs.2013.41006 Published Online January 2013 (http://www.scirp.org/journal/cs) Universal Current-Mode Biquad Filter Using a VDTA Dinesh Prasad 1* , Data Ram Bhaskar 1 , Mayank Srivastava 2 1 Department of Electronics and Communication Engineering, Faculty of Engineering and Technology, Jamia Millia Islamia, New Delhi, India 2 D/O Electronics and Communication Engineering, Amity School of Engineering and Technology, Amity University, Noida, India Email: * dprasad@jmi.ac.in, dbhaskar@jmi.ac.in, mayank2780@gmail.com Received October 9, 2012; revised November 9, 2012; accepted November 16, 2012 ABSTRACT This paper presents a new current-mode single input multi output (SIMO) type biquad employing one voltage differ- encing transconductance amplifier (VDTA), two grounded capacitors and a single grounded resistor. The configuration realizes all basic filter functions (i.e. Low Pass (LP), High Pass (HP), Band Pass (BP), Notch (BR) and All Pass (AP)). The natural frequency (ω 0 ) and bandwidth (BW) are independently tunable. The workability of proposed configuration has been verified using SPICE simulation with TSMC CMOS 0.18 μm process parameters. Keywords: Current Mode Filter; Voltage Differencing Transconductance Amplifier 1. Introduction Active filters are important basic building blocks, which are frequently employed in electrical engineering appli- cations. The current-mode approach [1] in designing ac- tive filters has become more popular due to its advanta- geous features such as larger dynamic range and wider bandwidth as compared to voltage-mode counterparts (particularly for the high frequency operations), simpler filtering configurations and lower power consumption. During the past few years, active filters using different current-mode/voltage-mode building blocks have been employed in which VDTA, recently introduced in [2], appears to be a useful active building block for an easy CMOS implementation of current-mode signal process- ing/signal generation [3-5]. Various SIMO-type active filters using different active elements are available in the literature see [6-13] and the references cited therein. In references [6-9], SIMO-type filter configurations employing 2/4 resistors and 2/3 ca- pacitors have been presented. These proposed filter struc- tures do not realize all the five filter responses. The con- figurations presented in [10] and [11] although use one resistor and two capacitors but fail to realize all the basic filter functions. Although the biquads proposed in [12] and [13] realize all the five filter functions but they use two capacitors along with 2/3 resistors. Therefore, the purpose of this communication is to propose a new SIMO-type current-mode universal biquad filter em- ploying one VDTA, two grounded capacitors and a sin- gle grounded resistor, which realizes all the basic filter functions i.e. LP, HP, BP, BR and AP. The natural fre- quency ω 0 and BW are independently tunable. The pro- posed circuit also offers low active and passive sensitivi- ties. The workability of proposed configuration has been verified using SPICE simulation with TSMC CMOS 0.18 μm process parameters. 2. The Proposed New Configurations The symbolic notation of the VDTA is shown in Figure 1, where V P and V N are input terminals and Z, X + and X − are output terminals. All terminals of VDTA exhibit high impedance values [2]. The VDTA can be described by the following set of equations: 1 1 2 2 0 0 0 0 0 P N m m V Z m V X m Z X g g V I I g V g V I                                        (1) The proposed circuit configuration is shown in Figure 2. A routine circuit analysis of Figure 2 yields the fol- lowing filter transfer functions:  1 2 1 1 m m o LP in g g I T s (2) I Ds     1 1 2 2 m o BP in g s C I T s I Ds         (3) * Corresponding author. Copyright © 2013 SciRes. CS