TABLE OF CONTENTS Steve Winder
| Note | You might not need a bandpass filter very often, but it's nice to know how to pull one out of your bag of tricks when you need it. I last used one a couple years ago, but I can cook one up as fast as I can apply solder! Here's a good cookbook from Steve Winder. Steve says he uses bandpass filters often in telecomm work, with a 300 Hz highpass to get rid of AC mains noise and a low-pass up to 3.4 kHz for antialiasing./rap |
There are two categories of bandpass filters: wideband and narrowband. Filters are classified as wideband if their upper and lower passband cutoff frequencies are more than an octave apart. This is when the upper frequency is over twice that of the lower frequency. Wideband filters are ideally constructed from lowpass and highpass filters connected in series. The denormalization and scaling process for these has already been described in Chapters 6 and 7. This chapter describes how to design narrowband analog active or passive bandpass filters. Narrowband filters have upper and lower frequencies that are an octave or less apart.
Passive bandpass filter designs will be based on the tables of normalized lowpass component values found in Chapter 2 of the last publication cited in the References section. Formulae will be given for the denormalization and scaling of these component values to produce a bandpass design. The equations are more complex than for lowpass or highpass transformations, but...
