cheb2ord

Design a Chebyshev II filter.

Syntax

[n,Wn] = cheb2ord(Wp,Ws,Rp,Rs,domain)

Inputs

Wp
A scalar specifying the passband frequency of a low or high pass filter, or a two element vector specifying the passband frequencies of a bandpass or bandstop filter. For a digital filter the values (in Hz) are normalized relative to the Nyquist frequency. For an analog filter the values are in radians/sec.
Ws
A scalar specifying the stopband frequency of a low or high pass filter, or a two element vector specifying the stopband frequencies of a bandpass or bandstop filter. For a digital filter the values (in Hz) are normalized relative to the Nyquist frequency. For an analog filter the values are in radians/sec.
Rp
The maximum attenuation in decibels at Wp.
Rs
The minimum attenuation in decibels at Ws.
domain
  • Use 'z' for digital filters (default).
  • Use 's' for analog filters.

Outputs

n
The lowest filter order that will meet the requirements.
Wn
Normalized frequency input for which the requirement is met.

Example

Design a digital Chebyshev II filter with no more than 1 dB attenuation at 100 Hz and at least 20 dB attenuation at 200 Hz, with a 1000 Hz sampling frequency.

[n,Wn] = cheb2ord(100/500, 200/500, 1, 20)
n = 3
Wn = 0.34336

Comments

In general, there are a range of corner frequencies for which the requirements can be met at the lowest order. Ws is the largest stopband meeting the design requirement. Wn is the smallest stopband meeting the design requirement.