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IIRFilters.ChebyshevIOrder Function
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Estimate the order a Chebyshev type I IIR filter.

Pascal
function ChebyshevIOrder(const BEdges: array of double; PassRipple: double; StopRipple: double; FilterType: TFilterType; var CutoffFreq: array of double; Analog: boolean = False): integer;
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Description

Returns the order of the Chebyshev type I filter. Bedg array must contain the band edges of the transition region(s) sorted in ascending order. PassRipple defines the ripple of the passband and StopRipple defines the ripple of the stopband. The length of the CutoffFreq array must be equal to one half of the length of the BEdg array and must match the specified FilterType. The routine returns the estimated order as a result and fill's the CutoffFreq array. This array can then be passed to the ChebyshevIFilter routine.

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Example

Design an analog highpass filter with transition band between 1 and 4 rad/sec and with at least 50dB attenuation at the end of the transition band and. The passband should not have more then 0.1dB ripple. 

 

  uses MtxExpr, Math387, MtxVec, SignalUtils, MtxVecTee, MtxVecEdit, IirFilters,
       LinearSystems;

  procedure TForm1.Button1Click(Sender: TObject);
  var z,p, num,den, FreqFr,Response: Vector;
      Order: integer;
      k,BW: double;
      WcArray: TDoubleArray; //modified 3dB frequency
  begin
      SetLength(WcArray,1);
      Order := ChebyshevIOrder([1,4],0.1,50,ftHighpass,WcArray,True);
      ChebyshevIAnalog(Order,0.1,z,p,k);  //design analog protype
      LowpassToHighpass(z,p,k,WcArray[0]);  //frequency transformation in s-domain
      ZeroPoleToTransferFun(num,den,z,p,k);
      FreqFr.Length := 1000;         //Define the frequency grid (logarithmic)
      LogRamp(FreqFr,-1,1); //between 0.1 (=10^(-1)) and 10 (=10^1) rad/sec
      FrequencyResponseS(num,den,FreqFr,Response); //Laplace
      DrawIt(Response); //Y axis linear, X axis logarithmic;
  end;

 

  #include "MtxExpr.hpp"
#include "MtxVecEdit.hpp"
#include "MtxVecTee.hpp"
#include "SignalUtils.hpp"
#include "IirFilters.hpp"
#include "LinearSystems.hpp"

void __fastcall TForm1::BitBtn1Click(TObject *Sender)
{
    sVector z,p, num,den, FreqFr, Response, WcArray;
    int Order;
    double k,Wc,BW;

    WcArray.Size(1);
    Order = ChebyshevIOrder(OPENARRAY(double,(1,4)),0.1,50,ftHighpass,WcArray.PValues1D(0),WcArray.Length-1,true);
    ChebyshevIAnalog(Order,0.1,z,p,k);  //design analog protype
    LowpassToHighpass(z,p,k,WcArray[0]);  //frequency transformation in s-domain
    ZeroPoleToTransferFun(num,den,z,p,k);
    FreqFr.Length = 1000;         //Define the frequency grid (logarithmic)
    LogRamp(FreqFr,-1,1); //between 0.1 (=10^(-1)) and 10 (=10^1) rad/sec
    FrequencyResponseS(num,den,FreqFr,Response); //Laplace
    DrawIt(Response); //Y axis linear, X axis logarithmic;
}
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