Butterworth濾波器設計（IIR類型）

• 設計濾波係數

打開MATLAB，選擇應用程序，點擊Filter Design & Analysis 

選擇Butterworth,設置階數，採樣頻率FS,截止頻率FC,最後點擊Design Filter確定

選擇Analysis菜單，點擊Filter Coefficients 

選擇Edit菜單，點擊Convert to single section

選擇Targets菜單，點擊Generate C Header... 

 選擇Export as，選擇single-precision float,點擊Generate

生成的文件內容如下 

/*
 * Filter Coefficients (C Source) generated by the Filter Design and Analysis Tool
 * Generated by MATLAB(R) 9.0 and the Signal Processing Toolbox 7.2.
 * Generated on: 27-Nov-2019 07:42:47
 */

/*
 * Discrete-Time IIR Filter (real)
 * -------------------------------
 * Filter Structure    : Direct-Form II
 * Numerator Length    : 7
 * Denominator Length  : 7
 * Stable              : Yes
 * Linear Phase        : No
 */

/* General type conversion for MATLAB generated C-code  */
#include "tmwtypes.h"
/* 
 * Expected path to tmwtypes.h 
 * C:\Program Files\MATLAB\R2016a\extern\include\tmwtypes.h 
 */
/*
 * Warning - Filter coefficients were truncated to fit specified data type.  
 *   The resulting response may not match generated theoretical response.
 *   Use the Filter Design & Analysis Tool to design accurate
 *   single-precision filter coefficients.
 */
const int NL = 7;
const real32_T NUM[7] = {
   0.004106325097,  0.02463795058,  0.06159487367,  0.08212649822,  0.06159487367,
    0.02463795058, 0.004106325097
};
const int DL = 7;
const real32_T DEN[7] = {
                1,   -2.021385193,    2.312567234,   -1.521253347,   0.6202822328,
    -0.1416414529,  0.01423505601
};

 C代碼實現Butterworlth濾波係數數組定義

float	FACTOR_B[] = {0.004106325097,  0.02463795058,  0.06159487367,  0.08212649822,  0.06159487367, 0.02463795058, 0.004106325097};
float	FACTOR_A[] = {1,   -2.021385193,    2.312567234,   -1.521253347,   0.6202822328,  -0.1416414529,  0.01423505601};	
	

 Butterworlth數據結構

typedef struct
{
	float xBuffer[FACTOR_NUMBER];
	float yBuffer[FACTOR_NUMBER];
}BUTTER_WORTH_BUFFER;

 Butterworth算法實現

static BUTTER_WORTH_BUFFER s_ecgFilter;
#define FACTOR_NUMBER 7

uint16_t buterworlthFilter(uint16_t x)
{
	uint32_t i;
	//運算之前Buf向前移動一個位置，以保存之前Buf的數據；
	for(i=FACTOR_NUMBER-1; i>0;i--)
	{
		s_ecgFilter.yBuffer[i] = s_ecgFilter.yBuffer[i-1];
		s_ecgFilter.xBuffer[i] = s_ecgFilter.xBuffer[i-1];
		
	}
	s_ecgFilter.xBuffer[0] = x;
	s_ecgFilter.yBuffer[0] = 0;
		
	for(i=1;i<FACTOR_NUMBER;i++)
	{
		s_ecgFilter.yBuffer[0] = s_ecgFilter.yBuffer[0]+FACTOR_B[i]*s_ecgFilter.xBuffer[i];
		s_ecgFilter.yBuffer[0] = s_ecgFilter.yBuffer[0]-FACTOR_A[i]*s_ecgFilter.yBuffer[i];
	}
	s_ecgFilter.yBuffer[0] = s_ecgFilter.yBuffer[0]+FACTOR_B[0]*s_ecgFilter.xBuffer[0];
	return (uint16_t)s_ecgFilter.yBuffer[0];
}