Design, Analysis and Applications of Some Signal Filters, Based on OP-AMP, on Different Environmental Conditions

Abstract

The design, analysis and operation of second order acti ve filters based on operati onal amplifiers, of the type LM3900, were investigated ex perimentall y, and simulated appl ying Electronic Work bench programs, and theoreti call y applying home developed computer progra ms. The study concerned wi th three types of second order acti ve filters, that is; l ow-pass (low-pass Butterworth second order acti ve fil ter and low-pass Chebyshev second order acti ve filter), high-pass (high-pass Butterworth second order active filter and high-pass Chebyshev second order acti ve filter) and band-pass second order active filter.

The stud y includes the design and excution of the d ifferent circuits, and the effects of each circu it element on the characteristics of the active fil ters. From which, the acti ve fi l ter electrical parameters; such as maximum gain, cutoff frequency (in case of low-pass and hi gh-pass fi l ters) or bandwidth (in case of band-pass fi l ter) and steepness factor were calculated. Also, a special program, namely: Electronic Work bench was applied for fi lter circuits simulation. In addition, special computer programs were developed to conform the previously obtained results.

The study was extended to i nclude the effect of tem perat ure on the characteristics of the operational amplifier and the filter circuits, in the range from room tem perature (1 7 °C) u p to 90 °C. It i s to be noted that the temperature variation causes the operational ampl ifier gain to decrease. As a result, the acti ve fi lters were shown to be sensi ti ve to temperature variation where their maxi mum gain, cutoff frequency and steepness factor were shown to be temperature dependent.