Practical Filter Design (4)

PRACTICAL FILTER DESIGN (4) by H. Baggott The previous part in this series discussed the most important low-pass filters. This month we turn our attention to high-pass and band-pass networks. Since these are derived from low-pass sections, we often speak of derived filters. A high-pass section is derived simply from a low-pass section by substituting 1/jcv in the transfer function for ja). This is not nearly as complicated as it looks, and is fairly easily realized in practical terms as well. In practice, it means that in a passive filter all inductances are re- placed by capacitances and all capacitances by inductances. In an active filter, all resistances and capacitances are interchanged. The computation of the new compo- nents is also simplicity itself. First, calculate the normalized values of all components for the low-pass section, re- place the components by their "op- posites" and compute the values of the newly required components as follows. Passive filters: CHP=1/L LP ...