RC Filters and RL Filters

Standard Filter Designs with Normalised Capacitor and Inductor Values

Standard or "normalised" values are available for filter designs based on the filter type (Chebyshev, Butterworth, Low-Pass, High-Pass etc) and the number of poles (which is usually the number of capacitors \ inductors in the circuit).

These normalised values are given for a cut-off frequency of 1 radian (links to http://www.mw0llo.com/mathematics/circular-measure.aspx) per second (which works out to be approximately 0.159 Hz) and a filter characteristic impedance of 1 Ω.

In order to build a practical filter, it is necessary to transform these normalised values into real values that can be used in the circuit. The equations below show how this is done.

Filter Reference Information