BilinearDesignLH.hpp

00001 //------------------------------------------------------------------------------
00002 //  Design of Butterworth LPF and HPF using bilinear transform -- Header
00003 //
00004 //   2014/06/29, Copyright (c) 2014 MIKAMI, Naoki
00005 //------------------------------------------------------------------------------
00006 
00007 #ifndef BILINEAR_BUTTERWORTH_HPP
00008 #define BILINEAR_BUTTERWORTH_HPP
00009 
00010 #include "mbed.h"
00011 #include <complex>  // requisite
00012 
00013 namespace Mikami
00014 {
00015     typedef complex<float> Complex; // define "Complex"
00016 
00017     class BilinearDesign
00018     {
00019     public:
00020         struct Coefs { float a1, a2, b1; };
00021         enum Type { LPF, HPF };
00022 
00023         // Constructor
00024         BilinearDesign(int order, float fs, Type pb)
00025             : PI_FS_(PI_/fs), ORDER_(order), PB_(pb)
00026         {
00027             sP_ = new Complex[order/2];
00028             zP_ = new Complex[order/2];
00029             ck_ = new Coefs[order/2];
00030         }
00031 
00032         // Destractor
00033         ~BilinearDesign()
00034         {
00035             delete[] sP_;
00036             delete[] zP_;
00037             delete[] ck_;
00038         }
00039 
00040         // Execution of design
00041         void Execute(float fc, Coefs c[], float& g);
00042 
00043     private:
00044         static const float PI_ = 3.1415926536f;
00045         const float PI_FS_;
00046         const int ORDER_;
00047         const Type PB_;
00048 
00049         Complex* sP_;   // Poles on s-plane
00050         Complex* zP_;   // Poles on z-plane
00051         Coefs* ck_;     // Coefficients of transfer function for cascade form
00052         float gain_;    // Gain factor for cascade form
00053 
00054         void Butterworth();
00055         void Bilinear(float fc);
00056         void ToCascade();
00057         void GetGain();
00058         void GetCoefs(Coefs c[], float& gain);
00059     };
00060 }
00061 #endif  // BILINEAR_BUTTERWORTH_HPP
00062