Analog Lowpass, Highpass, Bandpass, and Bandstop Filters - Practical Analog and Digital Filter Design - page 60

Butterworth Lowpass Filter
Selectivity: Lowpass
Approximation: Butterworth
Implementation: Analog
Passband gain (dB): -0.5
Stopband gain (dB): -21.0
Passband freq (Hz): 1000.0
Stopband freq (Hz): 2000.0
Filter Length/Order: 05
Overall Filter Gain: 1.00000000000E+00
Numerator Coefficients
QD [S^2 + S + 1 ]
== =========================================
01 0.0 0.00000000000E+00 7.75420567954E+03
02 0.0 0.00000000000E+00 6.01277057205E+07
03 0.0 0.00000000000E+00 6.01277057205E+07
Denominator Coefficients
QD [S^2 + S + 1 ]
== =========================================
01 0.0 1.00000000000E+00 7.75420567954E+03
02 1.0 4.79236266571E+03 6.01277057205E+07
03 1.0 1.25465683452E+04 6.01277057205E+07
Figure 3.2 Filter coefficients for Example 3.2 from WFilter.
Figure 3.3 Filter magnitude response for Example 3.2.
3.2 UNNORMALIZED HIGHPASS APPROXIMATION FUNCTIONS
The normalized lowpass approximation can also be used to generate the
approximation function for a highpass filter. The calculation for the ratio
frequency Ω r is based on the ratio of passband to stopband frequencies, as shown