kopia lustrzana https://github.com/Dsplib/libdspl-2.0
210 wiersze
6.3 KiB
C
210 wiersze
6.3 KiB
C
/*
|
||
* Copyright (c) 2015-2019 Sergey Bakhurin
|
||
* Digital Signal Processing Library [http://dsplib.org]
|
||
*
|
||
* This file is part of libdspl-2.0.
|
||
*
|
||
* is free software: you can redistribute it and/or modify
|
||
* it under the terms of the GNU Lesser General Public License as published by
|
||
* the Free Software Foundation, either version 3 of the License, or
|
||
* (at your option) any later version.
|
||
*
|
||
* DSPL is distributed in the hope that it will be useful,
|
||
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||
* GNU General Public License for more details.
|
||
*
|
||
* You should have received a copy of the GNU Lesser General Public License
|
||
* along with Foobar. If not, see <http://www.gnu.org/licenses/>.
|
||
*/
|
||
|
||
#include <stdio.h>
|
||
#include <stdlib.h>
|
||
#include <string.h>
|
||
#include "dspl.h"
|
||
|
||
|
||
#ifdef DOXYGEN_ENGLISH
|
||
/*! ****************************************************************************
|
||
\ingroup IIR_FILTER_DESIGN_GROUP
|
||
\fn int butter_ap(double Rp, int ord, double* b, double* a)
|
||
|
||
\brief
|
||
Function calculates the transfer function \f$ H(s) \f$ coefficients of
|
||
analog normalized lowpass Butterworth filter.
|
||
|
||
Analog normalized lowpass filter magnitude ripple equals \f$ -R_p \f$ dB
|
||
for angular frequency \f$ \omega \f$ from 0 to 1 rad/s.
|
||
|
||
\param[in] Rp
|
||
Magnitude ripple in passband (dB). \n
|
||
This parameter sets maximum filter distortion from 0 to 1 rad/s frequency. \n
|
||
Parameter must be positive. \n
|
||
\n
|
||
|
||
\param[in] ord
|
||
Filter order. \n
|
||
Filter coefficients number equals `ord+1` for numerator and denominator
|
||
of transfer function \f$ H(s) \f$ \n
|
||
\n
|
||
|
||
\param[out] b
|
||
Pointer to the vector of transfer function \f$H(s)\f$
|
||
numerator coefficient. \n
|
||
Vector size is `[ord+1 x 1]`. \n
|
||
Memory must be allocated. \n
|
||
\n
|
||
|
||
\param[out] a
|
||
Pointer to the vector of transfer function \f$H(s)\f$
|
||
denominator coefficient. \n
|
||
Vector size is `[ord+1 x 1]`. \n
|
||
Memory must be allocated. \n
|
||
\n
|
||
|
||
\return
|
||
`RES_OK` if filter coefficients is calculated successfully. \n
|
||
Else \ref ERROR_CODE_GROUP "code error".
|
||
\n
|
||
|
||
Example:
|
||
|
||
\include butter_ap_test.c
|
||
|
||
Result:
|
||
|
||
\verbatim
|
||
b[ 0] = 1.965 a[ 0] = 1.965
|
||
b[ 1] = 0.000 a[ 1] = 3.138
|
||
b[ 2] = 0.000 a[ 2] = 2.505
|
||
b[ 3] = 0.000 a[ 3] = 1.000
|
||
\endverbatim
|
||
\n
|
||
|
||
In `dat` folder will be created 3 files: \n
|
||
|
||
\verbatim
|
||
butter_ap_test_mag.txt magnitude
|
||
butter_ap_test_phi.txt phase response
|
||
butter_ap_test_tau.txt group delay
|
||
\endverbatim
|
||
|
||
In addition, GNUPLOT will build the following graphs from data stored in files:
|
||
|
||
\image html butter_ap_test.png
|
||
|
||
\author Sergey Bakhurin www.dsplib.org
|
||
***************************************************************************** */
|
||
#endif
|
||
#ifdef DOXYGEN_RUSSIAN
|
||
/*! ****************************************************************************
|
||
\ingroup IIR_FILTER_DESIGN_GROUP
|
||
\fn int butter_ap(double Rp, int ord, double* b, double* a)
|
||
|
||
\brief
|
||
Расчет передаточной характеристики \f$ H(s) \f$ аналогового
|
||
нормированного ФНЧ Баттерворта.
|
||
|
||
Функция рассчитывает коэффициенты передаточной характеристики \f$H(s)\f$
|
||
аналогового нормированного ФНЧ Баттерворта порядка `ord` с частотой среза
|
||
1 рад/с по уровню \f$ -R_p \f$ дБ.
|
||
|
||
\param[in] Rp
|
||
Неравномерность АЧХ в полосе пропускания (дБ). \n
|
||
Параметр задает уровень искажений в полосе от 0 до 1 рад/с. \n
|
||
Значение должно быть положительным. \n
|
||
\n
|
||
|
||
\param[in] ord
|
||
Порядок фильтра. \n
|
||
Количество коэффициентов числителя и знаменателя
|
||
передаточной функции \f$H(s)\f$ равно `ord+1`. \n
|
||
\n
|
||
|
||
\param[out] b
|
||
Указатель на вектор коэффициентов числителя
|
||
передаточной функции \f$H(s)\f$. \n
|
||
Размер вектора `[ord+1 x 1]`. \n
|
||
Память должна быть выделена. \n
|
||
\n
|
||
|
||
\param[out] a
|
||
Указатель на вектор коэффициентов знаменателя
|
||
передаточной функции \f$H(s)\f$. \n
|
||
Размер вектора `[ord+1 x 1]`. \n
|
||
Память должна быть выделена. \n
|
||
\n
|
||
|
||
\return
|
||
`RES_OK` --- фильтр рассчитан успешно. \n
|
||
В противном случае \ref ERROR_CODE_GROUP "код ошибки". \n
|
||
\n
|
||
|
||
Пример использования функции `butter_ap`:
|
||
|
||
\include butter_ap_test.c
|
||
|
||
Результат работы программы:
|
||
|
||
\verbatim
|
||
b[ 0] = 1.965 a[ 0] = 1.965
|
||
b[ 1] = 0.000 a[ 1] = 3.138
|
||
b[ 2] = 0.000 a[ 2] = 2.505
|
||
b[ 3] = 0.000 a[ 3] = 1.000
|
||
\endverbatim
|
||
\n
|
||
|
||
В каталоге `dat` будут созданы три файла: \n
|
||
|
||
\verbatim
|
||
butter_ap_test_mag.txt АЧХ фильтра
|
||
butter_ap_test_phi.txt ФЧХ фильтра
|
||
butter_ap_test_tau.txt ГВЗ фильтра
|
||
\endverbatim
|
||
|
||
Кроме того программа GNUPLOT произведет построение следующих графиков
|
||
по сохраненным в файлах данным:
|
||
|
||
\image html butter_ap_test.png
|
||
|
||
\author Бахурин Сергей www.dsplib.org
|
||
***************************************************************************** */
|
||
#endif
|
||
int DSPL_API butter_ap(double rp, int ord, double* b, double* a)
|
||
{
|
||
int res;
|
||
complex_t *z = NULL;
|
||
complex_t *p = NULL;
|
||
int nz, np;
|
||
|
||
if(rp < 0.0)
|
||
return ERROR_FILTER_RP;
|
||
if(ord < 1)
|
||
return ERROR_FILTER_ORD;
|
||
if(!a || !b)
|
||
return ERROR_PTR;
|
||
|
||
z = (complex_t*) malloc(ord*sizeof(complex_t));
|
||
p = (complex_t*) malloc(ord*sizeof(complex_t));
|
||
|
||
|
||
res = butter_ap_zp(ord, rp, z, &nz, p, &np);
|
||
if(res != RES_OK)
|
||
goto exit_label;
|
||
|
||
res = filter_zp2ab(z, nz, p, np, ord, b, a);
|
||
if(res != RES_OK)
|
||
goto exit_label;
|
||
|
||
b[0] = a[0];
|
||
|
||
|
||
exit_label:
|
||
if(z)
|
||
free(z);
|
||
if(p)
|
||
free(p);
|
||
return res;
|
||
}
|
||
|