Elliptic Filter

Syntax

Hd = ellip (Order, Frequencies, Rp, Rs, Type, DFormat)

Description

Classic IIR Elliptic filter design.

  • Equiripple in both the passband and stopband.
  • Fastest roll-off.
  • Lowest order filter of all supported prototypes.

Elliptic filter

Hd = ellip (Order, Frequencies, Rp, Rs, Type, DFormat)

Order: may be specified up to 20 (professional) and up to 10 (educational) edition. Setting the Order to 0, enables the automatic order determination algorithm.

Frequencies: lowpass and highpass filters have one transition band, and in as such require two frequencies (i.e. lower and upper cut-off frequencies of the transition band). For bandpass and bandstop filters, four frequencies are required (i.e. two transition bands). All frequencies must be ascending in order and < Nyquist (see the example below).

Rp: Passband ripple in dB.

Rs: Stopband attenuation in dB.

Type: The elliptic method facilitates the design of lowpass, highpass, bandpass and bandstop filters respectively.

Hd: the elliptic method designs an IIR Elliptic filter based on the entered specifications and places the transfer function (i.e. numerator, denominator, gain) into a digital filter object, Hd. The digital filter object can then be combined with other methods if so required. For a digital filter object, Hd, calling getnum(Hd), getden(Hd) and getgain(Hd) will extract the numerator, denominator and gain coefficients respectively – see below.

DFormat: allows you to specify the display format of resulting digital filter object.

symbolic Display a symbolic representation of the filter object. If the order > 10, the symbolic display option will be overridden and set to numeric.
numeric Display a matrix representation of the filter object.
void Create a filter object, but do not display output.

Example
ClearH1; // clear primary filter from cascade
ShowH2DM; // show DM on chart

Main()

Rp=1;
Rs=80;
F={50,120};
Hd=ellip(0,F,Rp,Rs,"lowpass","symbolic");

F={50,80,100,120};
Hd=ellip(0,F,Rp,Rs,"bandpass","symbolic");

Num = getnum(Hd); // define numerator coefficients
Den = getden(Hd); // define denominator coefficients
Gain = getgain(Hd); // define gain

See also

bessel / butter / cheby1 / cheby2 / ellip / arbmagphase / cplxfreqshift / dcremover / notch / peaking