BilinearDesignLH.hpp

00001 //------------------------------------------------------------------------
00002 //  Design of Butterworth LPF and HPF using bilinear transform -- Header
00003 //
00004 //   2017/03/25, Copyright (c) 2017 MIKAMI, Naoki
00005 //------------------------------------------------------------------------
00006 
00007 #ifndef BILINEAR_BUTTERWORTH_HPP
00008 #define BILINEAR_BUTTERWORTH_HPP
00009 
00010 #include "mbed.h"
00011 #include <complex>  // requisite
00012 #include "Array.hpp"
00013 
00014 namespace Mikami
00015 {
00016     typedef complex<float> Complex; // define "Complex"
00017 
00018     class BilinearDesign
00019     {
00020     public:
00021         struct Coefs { float a1, a2, b1, b2; };
00022         enum Type { LPF, HPF };
00023 
00024         // Constructor
00025         BilinearDesign(int order, float fs)
00026             : PI_FS_(PI_/fs), ORDER_(order),
00027               sP_(order/2), zP_(order/2), ck_(order/2) {}
00028 
00029         // Destractor
00030         virtual ~BilinearDesign() {}
00031 
00032         // Execution of design
00033         void Execute(float fc, Type pb, Coefs c[], float& g);
00034 
00035     private:
00036         static const float PI_ = 3.1415926536f;
00037         const float PI_FS_;
00038         const int ORDER_;
00039 
00040         Array<Complex> sP_; // Poles on s-plane
00041         Array<Complex> zP_; // Poles on z-plane
00042         Array<Coefs> ck_;   // Coefficients of transfer function for cascade form
00043         float gain_;        // Gain factor for cascade form
00044 
00045         void Butterworth();
00046         void Bilinear(float fc);
00047         void ToCascade(Type pb);
00048         void GetGain(Type pb);
00049         void GetCoefs(Coefs c[], float& gain);
00050     };
00051 }
00052 #endif  // BILINEAR_BUTTERWORTH_HPP