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Bessel filter app note issues

Question asked by J3627 on Mar 28, 2016

The information in this app note is not correct: http://www.analog.com/media/en/training-seminars/tutorials/MT-204.pdf

 

  • Bessel filters have a small amount of overshoot and ringing, not zero.  (Purely real pole filters and Gaussian filters have zero overshoot.)
  • The poles are the roots of the Bessel polynomials, which are neither on a circle nor equally spaced along the imaginary axis.  They are in an arc that looks somewhat circular, but not exactly, and the center of the circle would be in the right-hand plane, not at 0:

 

imageFile.png

 

The pole locations in Figure 7. Bessel Design Table are correct, but if you plot one of them you'll see they aren't on a circle, and the imaginary parts are not equally spaced:

 

2.2994-1.7395 = 0.5599

0.7335-0.2451 = 0.4884

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