Design of Butterworth Band-Pass Filter

Abstract

This paper presents a high order filter for the Butterworth filters up to 8th and 9th order. The higher order filters are formed by using the combination of second and third order filters. While designing the Band-Pass Butterworth filter, four parameters need to be specified such as Ap (dB attenuation in the pass band), As (dB attenuation in the stop band), fp (frequency at which Ap occurs) and fs (frequency at which As occurs). The design procedure involves two steps, the first step is to find the required order of the filter and the second step is to find the scale factor that must be applied to the normalized parameter values. The Band-Pass Butterworth filler is a combination between low pass and high pass For the low pass Butterworth filter, the value of a resistor that has been used are 100KΩ and the value of the capacitor is found by scaled inversely with the frequency and the selected resistor value. While for the high pass Butterworth filter, the value of a capacitor that has been used is 0.05µF and the resistor value is found by scaled inversely with the frequency and the selected resistor value. The Butterworth Band-Pass filler required to bypass certain band of interest while suppressing the frequency below and above than pass band. Two configurations design circuit was tested by using LTspice software.