Biquad.hpp

00001 //--------------------------------------------------------------
00002 // Biquad filter for IIR filter of cascade structure
00003 // Copyright (c) 2014 MIKAMI, Naoki, 2014/07/15
00004 //--------------------------------------------------------------
00005 
00006 #ifndef IIR_BIQUAD_HPP
00007 #define IIR_BIQUAD_HPP
00008 
00009 #include "mbed.h"
00010 
00011 namespace Mikami
00012 {
00013     // 2nd order IIR filter
00014     class Biquad
00015     {
00016     public:
00017         struct Coefs { float a1, a2, b1, b2; };
00018 
00019         Biquad() {}     // Default constructore
00020  
00021         Biquad(const Coefs ck)
00022             : a1_(ck.a1), a2_(ck.a2), b1_(ck.b1), b2_(ck.b2)
00023         { Clear(); }       
00024 
00025         float Execute(float xn)
00026         {
00027             float un = xn + a1_*un1_ + a2_*un2_;
00028             float yn = un + b1_*un1_ + b2_*un2_;
00029             
00030             un2_ = un1_;
00031             un1_ = un;
00032             
00033             return yn;
00034         }
00035  
00036         void Clear() { un1_ = un2_ = 0; }
00037  
00038     private:
00039         float a1_, a2_, b1_, b2_;
00040         float un1_, un2_;
00041  
00042         Biquad(const Biquad&);
00043     };
00044 }
00045 #endif  // IIR_BIQUAD_HPP