Engineering, 2010, 2, 179-183 doi:10.4236/eng.2010.23025 lished Online March 2010 (http://www.SciRP.org/journal/eng/) Copyright © 2010 SciRes. ENG Pub Tunable Bandwidth Third Order Switched-Capacitor with Multiple Feedbacks Filter for Different Center Frequencies Ganeshchandra N. Shinde 1 , Sanjay R. Bhagat 2 1 Indira Gandhi College Nanded, Maharashtra, India 2 Dnyanasadhana College , Thane, Maharashtra, India Email: shindegn@yahoo.co.in, sanjaybhagat_14@yahoo.co.in Received October 6, 2009; revised November 8, 2009; accepted November 13, 2009 Abstract This paper proposes third order tunable bandwidth active Switched-Capacitor filter. The circuit consists of only op-amps and switched capacitors. The circuit is designed for circuit merit factor Q = 10. The proposed circuit implements three filter functions low pass, band pass and high pass simultaneously in single circuit. The filter circuit can be used for both narrow as well as for wide bandwidth. For various values of cut-off frequencies the behaviour of circuit is studied. The circuit works properly only for higher central frequencies, when f 0 > 10 kHz. Keywords: Third Order Filter, Switched Capacitor, Pass Band Gain, Tunable Bandwidth, Circuit Merit Factor 1. Introduction Conventional analog circuits use the ratio of resistances to set the transfer function of filter circuits. The values of RC product determine the frequency responses of these circuits [1-4]. It is very difficult to make resistors and capacitors with the values and accuracy that are required in audio and instrumental applications. Resistors are ex- pensive and cannot be easily controlled [5]. The Switched-Capacitor concept can be used to realize a wide variety of universal filter that have the advantage of compactness and tunability [6]. In MOS integrated technology, it is relatively simple to achieve this objec- tive as compared to conventional techniques. It is due to high integration density, high precision and stability and ideal characteristics of MOSFET switches [7]. Switched capacitor techniques have been developed so that both digital and analog functions can be integrated on a single silicon chip. Switched capacitor filters are clocked sampled system. The input signal is sampled at a high rate and processed at a discrete time. Using these techniques resistors can be replaced by a capacitor and MOS switches that are rapidly turned on and off. Switched capacitor filters have the advantage of better accuracy in most of the cases [6-9]. Switched-Capacitor filters have the advantage of bet- ter accuracy in most cases. Typical center-frequency accuracies are normally on the order of about 0.2% for most Switched-Capacitor ICs, and worst-case numbers range from 0.4% to 1.5% (assuming, of course, that an accurate clock is provided). 2. Basic Switching Operation The essence of the Switched-Capacitor is the use of Ca- pacitors and analog Switches to perform the same func- tion as resistors. This replacement of resistor, analog with op. amp based integrator, then form an active filter [6]. Furthermore, the use of the Switched-Capacitor will be seen to give frequency tenability to active filters. Fil- ter using Switched-Capacitor technique overcome a ma- jor obstacle of filter on a chip fabrication—the imple- mentation of resistors by simulating resistors with high speed Switched-Capacitors using MOSFETs. The swit- ching function of the MOSFET produces a discrete resp- onse rather than a continuous response from the filter [6]. The operation of switched capacitor can be explained with the help of following circuit diagram: v 1 v 2  2  1 S 2 S 1 C S