Minimum order for elliptic filters
[n,Wp] = ellipord(Wp,Ws,Rp,Rs)
[n,Wp] = ellipord(Wp,Ws,Rp,Rs,'s')
ellipord
calculates the minimum order of
a digital or analog elliptic filter required to meet a set of filter
design specifications.
[n,Wp] = ellipord(Wp,Ws,Rp,Rs)
returns the lowest order, n
, of the
elliptic filter that loses no more than Rp
dB
in the passband and has at least Rs
dB
of attenuation in the stopband. The scalar (or vector) of corresponding
cutoff frequencies Wp
, is also returned. Use the
output arguments n
and Wp
in ellip
.
Choose the input arguments to specify the stopband and passband according to the following table.
Description of Stopband and Passband Filter Parameters
Use the following guide to specify filters of different types.
Filter Type Stopband and Passband Specifications
Filter Type  Stopband and Passband Conditions  Stopband  Passband 



 
Highpass 



Bandpass  The interval specified by 


Bandstop  The interval specified by 


If your filter specifications call for a bandpass or bandstop filter with unequal ripple in each of the passbands or stopbands, design separate lowpass and highpass filters according to the specifications in this table, and cascade the two filters together.
[n,Wp] = ellipord(Wp,Ws,Rp,Rs,'s')
finds the minimum order n
and cutoff
frequencies Wp
for an analog filter. You specify
the frequencies Wp
and Ws
similar
to those described in the Description of Stopband and Passband Filter
Parameters table
above, only in this case you specify the frequency in radians per
second, and the passband or the stopband can be infinite.
Use ellipord
for lowpass, highpass, bandpass,
and bandstop filters as described in the Filter Type Stopband and Passband Specifications table above.
[1] Rabiner, Lawrence R., and B. Gold. Theory and Application of Digital Signal Processing. Englewood Cliffs, NJ: PrenticeHall, 1975.