Chebyshev Type I analog lowpass filter prototype
Frequency Response of an Analog Chebyshev Type I Filter
Design a 6th-order Chebyshev Type I analog lowpass filter with 3 dB of ripple in the passband. Display its magnitude and phase responses.
[z,p,k] = cheb1ap(6,3); % Lowpass filter prototype [num,den] = zp2tf(z,p,k); % Convert to transfer function form freqs(num,den) % Frequency response of analog filter
n — Filter order
Filter order, specified as an integer.
Rp — Passband ripple
Passband ripple, specified as a scalar in decibels.
Chebyshev Type I filters are equiripple in the passband and monotonic in the stopband. The poles are evenly spaced about an ellipse in the left half plane. The Chebyshev Type I passband edge angular frequency ω0 is set to 1.0 for a normalized result. This value is the frequency at which the passband ends. The filter has a magnitude response of 10–Rp/20.
The transfer function is given by
 Parks, Thomas W., and C. Sidney Burrus. Digital Filter Design. New York: John Wiley & Sons, 1987.
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Usage notes and limitations:
All inputs must be constants. Expressions or variables are allowed if their values do not change.