Design and Analysis of Different Orders of Active-RC Butterworth Filter

Abstract

Recently, developments in wireless communication have motivated many design challenges. As a critical block of wireless devices, baseband filters operating with kilohertz to a few megahertz cut-off frequencies significantly contribute to the overall power consumption of receivers. One basic circuit used in these systems is a filter. All the filters are designed in a different way depending upon the application for which they are being designed. Filters can be classified on the basis of response characteristics, components used, mathematical approximations or digital and analog filters. On the basis of mathematical approximation one type i.e. Butterworth filter is the most popular and widely used filter. Active-RC Butterworth filter is a basic filter that is widely used for anti-aliasing and for channel filtering. For lower order of filters this filter is very commonly used. In Active-RC filter, an active device has to be chosen for a desirable response of the filter. There is a range of devices like Operational Amplifier, Difference Differential Amplifier, Operational Transconductor Amplifier etc. can be used to design an Active- RC filter. After extensive study, of all the choices Operational Transconductor Amplifier is chosen to design an active-RC Butterworth filter. Amongst all the topologies of OTA (Operational Transconductor Amplifier), on the basis of literature survey, Telescopic OTA, is chosen. The design procedure for a Single stage Telescopic OTA is developed using design equations. The circuit designed is then simulated on Tanner EDA tool. The simulated results are validating the theoretical values. The Active-RC Butterworth filter design steps are developed, beginning right from the selection of active device to the final filter response. The result of the 6th order active-RC Butterworth filter schematic is then compared with the layout drawn on Tanner EDA tool. The passband frequency response achieved after simulation well- justifies that the filter may be used for video frequency applications. With the increase in filter order many parameters change. Few of them are calculated and observed by designing different orders of filters and analyzing them. Analysis is done in terms of change in roll-off rates, passband frequency achieved and the power dissipation. The results of the analysis are in accordance with the literature.