Passive Analogue Filter Development - Modern Practice

Modern Practice

LC passive filters gradually became less popular as active amplifying elements, particularly operational amplifiers, became cheaply available. The reason for the change is that wound components (the usual method of manufacture for inductors) are far from ideal, the wire adding resistance as well as inductance to the component. Inductors are also relatively expensive and are not "off-the-shelf" components. On the other hand, the function of LC ladder sections, LC resonators and RL sections can be replaced by RC components in an amplifier feedback loop (active filters). These components will usually be much more cost effective, and smaller as well. Cheap digital technology, in its turn, has largely supplanted analogue implementations of filters. However, there is still an occasional place for them in the simpler applications such as coupling where sophisticated functions of frequency are not needed.