Filtering and electrical filters

Filtering, which consists in isolating a frequency band from a complex signal, is one of the most widely used functions in electronic assemblies and signal processing. Most electronic systems include a large number of filters to meet a wide variety of functional requirements.

In very general terms, filtering is a form of signal processing, obtained by sending the useful signal through a set of electronic circuits, which modify its frequency spectrum, and/or its phase, and therefore its shape (figure 1 ). The purpose of filtering is to extract part of the information associated with this signal, or more often, to restore a more intelligible signal from an incident signal, in terms of the information it contains and which we wish to select. This may involve eliminating or attenuating unwanted interference frequencies, or isolating the useful frequency band(s) in a complex signal.

Finally, an electrical filter effects a change from an electrical input signal, for example a voltage v ₁ (t), to an electrical output signal, namely a voltage v ₂ (t). To the modification of the time signal v ₁ (t) corresponds a modification of the spectrum V ₁ (jω) to produce a new spectrum V ₂ (jω) associated with the signal v ₂ (t).