bsf_2.h

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 * @details
 * This file defines the @ref filter::band_stop::BSF_2 class, which
 * implements a discrete-time second-order band-stop filter.
 *
 * The filter attenuates frequency components within a specified
 * frequency band while allowing frequencies below and above the
 * stopband to pass.
 *
 * The filter is parameterized by its center frequency, bandwidth,
 * and sampling time. The quality factor is derived from the center
 * frequency and bandwidth.
 *
 * The implementation maintains previous input and output samples as
 * internal filter state.
 *
 * The class is templated to support different numeric types such as
 * @c float and @c double.
 *
 * @tparam T Numeric data type used for the filter calculations.
 *
 * @author Abhinay Kumar
 * @version 1.0.0
 *
 * @copyright
 * Copyright (c) 2026 Abhinay Kumar
 */
 
#ifndef FILTER_BSF_2_H
#define FILTER_BSF_2_H
 
#include <cstdint>
#include <cmath>
 
namespace filter
{
 
    namespace band_stop
    {

         * @details
         * The BSF_2 class implements a discrete-time second-order
         * band-stop filter.
         *
         * The filter attenuates frequency components around the specified
         * center frequency while allowing frequencies outside the stopband
         * to pass.
         *
         * The filter is configured using the center frequency, bandwidth,
         * and sampling time. The quality factor is calculated from the
         * center frequency and bandwidth.
         *
         * @tparam T Numeric data type used for the filter.
         *
         * @par Example
         * @code{.cpp}
         * filter::band_stop::BSF_2<double> filter;
         *
         * filter.config(50.0, 5.0, 0.001);
         *
         * double output = filter.update(input);
         * @endcode
         */
        template <typename T>
        class BSF_2
        {
        public:
             * state initialized to their default values.
             */
            BSF_2();


             *
             * @param[in] f0_ Center frequency of the filter in Hz.
             * @param[in] B_ Bandwidth of the filter in Hz.
             * @param[in] dt_ Sampling time of the filter in seconds.
             *
             * @details
             * Configures the filter using the specified center frequency,
             * bandwidth, and sampling time, and calculates the required
             * filter coefficients.
             */
            void config(T f0_, T B_, T dt_);

            /**
             * @brief Sets the filter parameters.
             *
             * @param[in] f0_ Center frequency of the filter in Hz.
             * @param[in] B_ Bandwidth of the filter in Hz.
             * @param[in] dt_ Sampling time of the filter in seconds.
             *
             * @details
             * Updates the center frequency, bandwidth, and sampling time
             * used by the filter.
             */
            void set_param(T f0_, T B_, T dt_);


             * @return Filtered output sample.
             *
             * @details
             * Processes the current input sample using the second-order
             * band-stop filter equation and updates the internal filter
             * state.
             */
            T update(T x_k);


             * @details
             * Resets the previous input and output samples and the
             * startup counter.
             */
            void reset();

            void set_f0(T f0_);

            void set_B(T B_);

            void set_dt(T dt_);

            T get_f0();

            T get_B();

            T get_dt();

            T get_Q();

            T get_fs();
 
        private:
            T f0 = 0.0;

            T B = 0.0;

            T dt = 0.0;

            T Q = 0.0;

            T lambda_1 = 0.0;

            T lambda_2 = 0.0;

            T lambda_3 = 0.0;

            T lambda_4 = 0.0;

            T lambda_5 = 0.0;

            T y_k_1 = 0.0;

            T y_k_2 = 0.0;

            T x_k_1 = 0.0;

            T x_k_2 = 0.0;

            uint8_t start_counter = 0;

            T prewarp_freq(T wc_, T dt_);
        };
 
#include "../../src/band_stop/bsf_2.tpp"
 
    } // namespace band_stop
 
} // namespace filter
 
#endif // FILTER_BSF_2_H