EVALUATION OF THE PERFORMANCE OF CASCADED BUTTERWORTH FILTER

CHAPTER ONE 1.0 INTRODUCTION A filter is a network designed to pass signals at certain frequencies, and to reject signals at all other frequencies. Ideally, a filter would introduce zero attenuation to selected frequencies, known as the pass band and completely block all others (the stop band). Since a filter has to be frequency sensitive, it must employ frequency dependent components such as inductors or capacitors or usually a combination of both. There are four basic types of filter namely: Low-pass, High-pass, Band-pass and Band-stop. In addition, a filter circuit may be classified as being either passive or active. A passive filter is one which contains only a combination of resistors, inductors and capacitors but no power source within it. An active filter consists of a combination of these components interconnected with an operational amplifier (op-amp). The latter would include its own power supply source, independent of the signal to be filtered (Robertson, 1993). Filter plays a very important role in the field of electronics and telecommunication, since there is always a need to separate frequency component. Electronic filters are electronic circuits which perform signal processing function specifically to remove unwanted frequency components from the signal and to enhance wanted ones. (Andrew, 2006). The development of electric wave filters traced back to the early long-distance telegraph cables. These solid dielectric cables had high capacitance which slowed the time of signals and severely limited message transmission speed. The fundamental principles of electric filters were outlined by Wagner in Germany and Campbell in USA around 1915. However, the practical filters did not meet those ideal filters because the alternation was higher at the band edge and pass band impedance was different from that of constant resistance elements. The choice of a particular type of filter from the large range of filters must be influenced by several factors which include: complexity, ease of tuning, economic, compatibility with existing circuitry and power supply. Filter networks are widely used in communication systems to separate various voice channels in carrier frequent telephone circuits. Filters also find applications in instrumentation, telemetering equipment e.t.c. where it is necessary to transmit or alternate a limited range of frequencies. (Sudlakar and Palli, 2008). 1.1 SIGNIFICANCE OF THE PROJECT Filters are widely used in circuits such as amplifiers, oscillators and power supplies to give the required frequency characteristics. Optimum performances from these circuits are always difficult due to disturbances from external sources or in-built circuit. These disturbances are minimized by the use of filters so as to obtain performances close to the ideal and so the need for the study of filters. 1.2 SCOPE OF THE PROJECT This project is focused on 6th order low-pass Butterworth filter so as to obtain a filtering device that will have a frequency response that is maximally flat. 1.3 AIM AND OBJECTIVES The aim of this project is to evaluate the performances of a 6th Order Butterworth low-pass filter. The objectives to be obtained are; • To design a 6th order active Butterworth filter using the transfer function method. • To measure the parameters that will be used to obtain the filter characteristics such as transfer function, bandwidth, propagation constant, propagation constant, selectivity, phase angle and characteristics impedance.

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