Indian Journal of Pure & Applied Physics Vol. 42, May 2004, pp 375-377 Note Current-mode universal filter using current feedback amplifiers N A Shah, M F Rather & S Z Iqbal Postgraduate Department of Electronics & Instrumentation Technology, The University of Kashmir, Srinagar 190006 Email: nassgr@hotmail.com Received 14 May 2003; accepted 25 November 2003 A new current-mode (CM) universal filter based on and employing three each of non-inverting current feedback amplifiers (CFAs), capacitors, and resistors is presented. Without changing the circuit topology the output currents simultaneously supports lowpass (LP), highpass (HP), and bandpass (BP) responses. The notch (BR) and allpass (AP) filtering functions can be achieved by connecting the appropriate nodes without requiring the use of additional components. The proposed circuit enjoys low passive sensitivities and orthogonal tuning of the parameters natural frequency,ω 0 and quality factor, Q. Personal computer-simulation programme with integrated circuit emphasis (PSPICE) simulated results agree well with calculated values. [Keywords: Current-mode filters, Universal filters] IPC Code: H 03 H 7/075 CM filters have received growing interest 1-9 owing to their performances in terms of wider bandwidth, wider dynamic range and greater linearity compared to voltage-mode (VM) counterparts 10-11 . The CFA is a four terminal building block which has distinct features of high slew rate and the constant bandwidth which is independent of closed-loop gain. Many active resistor-capacitor (RC)-filters using CFAs have been reported in the literature 12-17 which operate either in VM or in CM. A very few CM filters constructed around CFA have been reported in the literature. The reported papers 18-19 operate both in VM and in CM, but have the drawbacks of realizing notch and AP responses with the addition of current inverter. This paper presents a universal biquad filtering circuit operating in CM. The proposed circuit has been developed around three CFAs and five grounded and one floating passive elements. The circuit can realize LP, BP, and HP responses simultaneously; however, notch and AP filtering signals can be realized by connecting the appropriate nodes. The cut off frequency, ω 0 can be adjusted independent of quality factor, Q, in a sequential manner. The sensitivity figures are small, thereby ensuring improved performance of the circuit. Circuit description ⎯ The CFA is characterized by the port relations V x = V y I x = I z , I y = 0, and V 0 = V z …(1) The proposed universal filter is depicted in Fig. 1. Using the preceding port relations the current transfer functions realized by this filter are given by () s D R R R I I In LP 4 2 1 1 − = … (2) () s D R R C s I I In BP 4 2 6 = … (3) () s D R C C s I I In HP 1 5 3 2 − = … (4) where () 4 2 1 4 2 6 1 5 3 2 1 R R R R R C s R C C s s D + + = Therefore, LP, BP, and HP responses can be simultaneously obtained from this filter. By connecting together I HP and I LP the Notch function results which is given by () s D R R R R C C s I I In N 4 2 1 1 5 3 2 1 + − = …(5)