diff options
Diffstat (limited to 'macros/ellipord.sci')
| -rw-r--r-- | macros/ellipord.sci | 125 |
1 files changed, 91 insertions, 34 deletions
diff --git a/macros/ellipord.sci b/macros/ellipord.sci index cc81ab7..f0c52a4 100644 --- a/macros/ellipord.sci +++ b/macros/ellipord.sci @@ -1,36 +1,93 @@ +// Copyright (C) 2018 - IIT Bombay - FOSSEE +// +// This file must be used under the terms of the CeCILL. +// This source file is licensed as described in the file COPYING, which +// you should have received as part of this distribution. The terms +// are also available at +// http://www.cecill.info/licences/Licence_CeCILL_V2-en.txt +// Original Source : https://octave.sourceforge.io/signal/ +// Modifieded by:Sonu Sharma, RGIT Mumbai +// Organization: FOSSEE, IIT Bombay +// Email: toolbox@scilab.in + function [n, Wp] = ellipord(Wp, Ws, Rp, Rs) -//This function computes the minimum filter order of an elliptic filter with the desired response characteristics. -//Calling Sequence -//[n] = ellipord(Wp, Ws, Rp, Rs) -//[n, Wp] = ellipord(Wp, Ws, Rp, Rs) -//Parameters -//Wp: scalar or vector of length 2, all elements must be in the range [0,1] -//Ws: scalar or vector of length 2, all elements must be in the range [0,1] -//Rp: real or complex value -//Rs: real or complex value -//Description -//This is an Octave function. -//This function computes the minimum filter order of an elliptic filter with the desired response characteristics. -//Stopband frequency ws and passband frequency wp specify the the filter frequency band edges. -//Frequencies are normalized to the Nyquist frequency in the range [0,1]. -//Rp is measured in decibels and is the allowable passband ripple and Rs is also measured in decibels and is the minimum attenuation in the stop band. -//If ws>wp then the filter is a low pass filter. If wp>ws, then the filter is a high pass filter. -//If wp and ws are vectors of length 2, then the passband interval is defined by wp and the stopband interval is defined by ws. -//If wp is contained within the lower and upper limits of ws, the filter is a band-pass filter. If ws is contained within the lower and upper limits of wp, the filter is a band-stop or band-reject filter. -//Examples -//[a,b]=ellipord(0.2, 0.5, 0.7, 0.4) -//a = 1 -//b = 0.20000 - -rhs = argn(2) -lhs = argn(1) -if(rhs~=4) -error("Wrong number of input arguments.") -end -select(lhs) -case 1 then -n = callOctave("ellipord",Wp,Ws,Rp,Rs) -case 2 then -[n,Wp] = callOctave("ellipord",Wp,Ws,Rp,Rs) -end + //Minimum filter order of a digital elliptic or Cauer filter with the desired response characteristics. + + //Calling Sequence + //[n] = ellipord(Wp, Ws, Rp, Rs) + //[n, Wp] = ellipord(Wp, Ws, Rp, Rs) + + //Parameters + //Wp: scalar or vector of length 2 (passband edge(s)), all elements must be in the range [0,1] + //Ws: scalar or vector of length 2 (stopband edge(s)), all elements must be in the range [0,1] + //Rp: passband ripple in dB. + //Rs: stopband attenuation in dB. + //n: Minimum order of filter satisfying given specs. + + //Description + //This function computes the minimum filter order of an elliptic filter with the desired response characteristics. + //Stopband frequency ws and passband frequency wp specify the the filter frequency band edges. + //Frequencies are normalized to the Nyquist frequency in the range [0,1]. + //Rp is measured in decibels and is the allowable passband ripple and Rs is also measured in decibels and is the minimum attenuation in the stop band. + //If ws>wp then the filter is a low pass filter. If wp>ws, then the filter is a high pass filter. + //If wp and ws are vectors of length 2, then the passband interval is defined by wp and the stopband interval is defined by ws. + //If wp is contained within the lower and upper limits of ws, the filter is a band-pass filter. If ws is contained within the lower and upper limits of wp, the filter is a band-stop or band-reject filter. + //Examples + //Wp = [60 200]/500; + //Ws = [50 250]/500; + //Rp = 3; + //Rs = 40; + //[n,Wp] = ellipord(Wp,Ws,Rp,Rs) + //Output : + // Wp = + // + // 0.12 0.4 + // n = + // + // 5. + + funcprot(0); + [nargout nargin] = argn(); + + if (nargin ~= 4) + error("ellipord: invalid number of inputs"); + else + validate_filter_bands ("ellipord", Wp, Ws); + end + + // sampling frequency of 2 Hz + T = 2; + + Wpw = tan(%pi.*Wp./T); // prewarp + Wsw = tan(%pi.*Ws./T); // prewarp + + // pass/stop band to low pass filter transform: + if (length(Wpw)==2 & length(Wsw)==2) + wp=1; + w02 = Wpw(1) * Wpw(2); // Central frequency of stop/pass band (square) + w3 = w02/Wsw(2); + w4 = w02/Wsw(1); + if (w3 > Wsw(1)) + ws = (Wsw(2)-w3)/(Wpw(2)-Wpw(1)); + elseif (w4 < Wsw(2)) + ws = (w4-Wsw(1))/(Wpw(2)-Wpw(1)); + else + ws = (Wsw(2)-Wsw(1))/(Wpw(2)-Wpw(1)); + end + elseif (Wpw > Wsw) + wp = Wsw; + ws = Wpw; + else + wp = Wpw; + ws = Wsw; + end + + k=wp/ws; + k1=sqrt(1-k^2); + q0=(1/2)*((1-sqrt(k1))/(1+sqrt(k1))); + q= q0 + 2*q0^5 + 15*q0^9 + 150*q0^13; //(....) + D=(10^(0.1*Rs)-1)/(10^(0.1*Rp)-1); + + n=ceil(log10(16*D)/log10(1/q)); + endfunction |