English
- //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- //
- // File = chebyshev_proto.cpp
- //
- // Prototype Chebyshev (Type I) Filter
- //
- #include <math.h>
- #include "misdefs.h"
- #include "parmfile.h"
- #include "chebyshev_proto.h"
- #include "filter_types.h"
- extern ParmFile ParmInput;
- #ifdef _DEBUG
- extern ofstream *DebugFile;
- #endif
- //======================================================
- // constructor
- ChebyshevPrototype::ChebyshevPrototype( int filt_order,
- double ripple,
- bool bw_is_ripple_bw )
- :AnalogFilterPrototype( filt_order )
- {
- Ripple = ripple;
- Bw_Is_Ripple_Bw = bw_is_ripple_bw;
- Bw_Is_3db_Bw = !bw_is_ripple_bw;
- //=========================================================
- // Computes poles for normalized ChebyshevPrototype prototype
- int k;
- double x;
- double epsilon;
- double gamma;
- double sigma_mult;
- double omega_mult;
- double a_factor, r_factor;
- std::complex<double> work;
- Pole_Locs = new std::complex<double>[Filt_Order+1];
- Pole_Locs[0] = Filt_Order;
- Num_Poles = Filt_Order;
- Zero_Locs = new std::complex<double>[1];
- Zero_Locs[0] = 0;
- Num_Zeros = 0;
- epsilon = sqrt(pow(10.0, (Ripple/10.0))-1.0);
- if(Bw_Is_3db_Bw)
- {
- a_factor = log((1+sqrt(1.0-epsilon*epsilon))/epsilon)/Filt_Order;
- r_factor = cosh(a_factor);
- }
- gamma = pow( (1+sqrt(1.0 + epsilon*epsilon))/epsilon,
- 1.0/double(Filt_Order));
- sigma_mult = ( (1.0/gamma) - gamma) / 2.0;
- omega_mult = ( (1.0/gamma) + gamma) / 2.0;
- for( k=1; k<=Filt_Order; k++)
- {
- x = PI * ((2*k)-1) / (2*Filt_Order);
- Pole_Locs[k-1] = std::complex<double>( sigma_mult*sin(x), omega_mult*cos(x));
- if(Bw_Is_3db_Bw) Pole_Locs[k-1] /= r_factor;
- }
- //-----------------------------------------
- // Compute Biquads
- Num_Biquad_Sects = (Filt_Order-(Filt_Order%2))/2;
- //Biquad_Coef_A = new double[Num_Biquad_Sects];
- B1_Coef = new double[Num_Biquad_Sects];
- B0_Coef = new double[Num_Biquad_Sects];
- if(Filt_Order%2)
- { // order is odd
- Real_Pole = Pole_Locs[Num_Biquad_Sects].real();
- }
- for( k=1; k<=Num_Biquad_Sects; k++)
- {
- x = PI * ((2*k)-1) / (2*Filt_Order);
- //Biquad_Coef_A[k-1] = 1.0;
- B1_Coef[k-1] = -2.0 * sigma_mult * sin(x);
- B0_Coef[k-1] = (0.25/(gamma*gamma)) +
- gamma * gamma / 4.0 +
- 0.5 * cos(2.0 * x);
- }
- //-----------------------------------------
- // Compute gain factor Ho
- work = 1.0;
- for( k=0; k<Filt_Order; k++)
- {
- work *= (-Pole_Locs[k]);
- }
- //H_Zero = std::real<double>(work);
- H_Zero = work.real();
- if(Filt_Order%2 == 0) // if order is even
- {
- H_Zero /= pow(10.0, Ripple/20.0);
- }
- //if(Bw_Is_3db_Bw)
- // {
- // H_Zero *= r_factor;
- // }
- #ifdef _DEBUG
- int i;
- for(i=0; i<filt_order; i++)
- {
- *DebugFile << "pole[" << i << "] = ("
- << Pole_Locs[i].real() << ", "
- << Pole_Locs[i].imag() << ")" << endl;
- }
- #endif
- return;
- }
- //==========================================================
- ChebyshevPrototype::~ChebyshevPrototype()
- {
- }
