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Diffstat (limited to 'macros/cheb2ord.sci')
| -rw-r--r-- | macros/cheb2ord.sci | 125 |
1 files changed, 91 insertions, 34 deletions
diff --git a/macros/cheb2ord.sci b/macros/cheb2ord.sci index 815ba0d..27ca7e6 100644 --- a/macros/cheb2ord.sci +++ b/macros/cheb2ord.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, Wc] = cheb2ord(Wp, Ws, Rp, Rs) -//This function computes the minimum filter order of a Chebyshev type II filter with the desired response characteristics. -//Calling Sequence -//n = cheb2ord(Wp, Ws, Rp, Rs) -//[n, Wc] = cheb2ord(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 value -//Rs: real value -//Description -//This is an Octave function. -//This function computes the minimum filter order of a Chebyshev type II 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 -//cheb2ord([0.25,0.3],[0.2,0.8],0.3,0.4) -//ans = 1 - -rhs = argn(2) -lhs = argn(1) -if(rhs~=4) -error("Wrong number of input arguments.") -end - - select(lhs) - case 1 then - n = callOctave("cheb2ord",Wp,Ws,Rp,Rs) - case 2 then - [n,Wc] = callOctave("cheb2ord",Wp,Ws,Rp,Rs) - end + //Minimum filter order of a digital Chebyshev type II filter with the desired response characteristics. + + //Calling Sequence + //n = cheb2ord(Wp, Ws, Rp, Rs) + //[n, Ws] = cheb2ord(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 a Chebyshev type II 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 = 40/500; + //Ws = 150/500; + //Rp = 3; + //Rs = 60; + //[n,Ws] = cheb2ord(Wp,Ws,Rp,Rs) + //Output : + // Ws = + // + // 0.3 + // n = + // + // 4. + // + + funcprot(0); + [nargout nargin] = argn(); + + if nargin ~= 4 + error("cheb2ord: invalid number of inputs") + else + validate_filter_bands ("cheb2ord", Wp, Ws); + end + + T = 2; + + // returned frequency is the same as the input frequency + Wc = Ws; + + // warp the target frequencies according to the bilinear transform + Ws = (2/T)*tan(%pi*Ws./T); + Wp = (2/T)*tan(%pi*Wp./T); + + if (Wp(1) < Ws(1)) + // low pass + if (length(Wp) == 1) + Wa = Wp/Ws; + else + // FIXME: Implement band reject filter type + error ("cheb2ord: band reject is not yet implemented"); + end + else + // if high pass, reverse the sense of the test + if (length(Wp) == 1) + Wa = Ws/Wp; + else + // band pass + Wa=(Wp.^2 - Ws(1)*Ws(2))./(Wp*(Ws(1)-Ws(2))); + end; + end; + Wa = min(abs(Wa)); + + // compute minimum n which satisfies all band edge conditions + stop_atten = 10^(abs(Rs)/10); + pass_atten = 10^(abs(Rp)/10); + n = ceil(acosh(sqrt((stop_atten-1)/(pass_atten-1)))/acosh(1/Wa)); + endfunction |