Chapter 5 - Highpass filters

Abstract

This chapter describes how to design an analog active or passive highpass filter having almost any desired specification. Examples of types of highpass filter and formulae for the denormalization of component are provided. Passive highpass filters are designed using the normalized lowpass model. Converting the lowpass model into a highpass equivalent is not too demanding in all-pole filters, like Butterworth or Chebyshev types. The process requires replacing each inductor in the lowpass model by a capacitor. Similarly, each capacitor in the lowpass model has to be replaced by an inductor. The denormalization of the highpass model for higher load impedance requires component values to be scaled in order to have higher impedance. This process is identical to that of denormalizing a lowpass filter. Active filters use pole and zero locations from the frequency response's transfer function. A lowpass to highpass translation is required to find the highpass normalized pole and zero locations. The pole and zero locations are used to find component values. Basic highpass active filter designs are reviewed in the chapter.