Practical design considerations for a variable center frequency, constant bandwidth, and constant peak-value active filter

Frequency active filters are designed by treating the operational amplifier as ideal. Consequently, the actual circuit´s performance may depart considerably from what is expected. This is demonstrated in the design of an active bandpass circuit. However, it is shown that good agreement results between the predicted and actual performance if the operational amplifier´s frequency dependence and output resistance are taken into account. Expressions are derived for the pole shift caused by the nonideal amplifier. Subject to given constraints, quantitative results are given that establish an upper bound on the frequency of operation of the bandpass circuit.