quadrature_demod_cf.h

Go to the documentation of this file.

/* -*- c++ -*- */
/*
 * Copyright 2004,2012 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 */
 
#ifndef INCLUDED_ANALOG_QUADRATURE_DEMOD_CF_H
#define INCLUDED_ANALOG_QUADRATURE_DEMOD_CF_H
 
#include <gnuradio/analog/api.h>
#include <gnuradio/sync_block.h>
 
namespace gr {
namespace analog {
 
/*!
 * \brief quadrature demodulator: complex in, float out
 * \ingroup modulators_blk
 *
 * \details
 * This can be used to demod FM, FSK, GMSK, etc.  The input is complex
 * baseband, output is the signal frequency in relation to the sample
 * rate, multiplied with the gain.
 *
 * Mathematically, this block calculates the product of the one-sample
 * delayed input and the conjugate undelayed signal, and then calculates
 * the argument of the resulting complex number:
 *
 * \f$y[n] = \mathrm{arg}\left(x[n] \, \bar x [n-1]\right)\f$.
 *
 * Let \f$x\f$ be a complex sinusoid with amplitude \f$A>0\f$, (absolute)
 * frequency \f$f\in\mathbb R\f$ and phase \f$\phi_0\in[0;2\pi]\f$ sampled at
 * \f$f_s>0\f$ so, without loss of generality,
 *
 * \f$x[n]= A e^{j2\pi( \frac f{f_s} n + \phi_0)}\f$
 *
 * then
 *
 * \f{align*}{ y[n] &= \mathrm{arg}\left(A e^{j2\pi\left( \frac f{f_s} n + \phi_0\right)}
 * \overline{A e^{j2\pi( \frac f{f_s} (n-1) + \phi_0)}}\right)\\
 *  & = \mathrm{arg}\left(A^2 e^{j2\pi\left( \frac f{f_s} n + \phi_0\right)} e^{-j2\pi(
 * \frac f{f_s} (n-1) + \phi_0)}\right)\\
 *  & = \mathrm{arg}\left( A^2 e^{j2\pi\left( \frac f{f_s} n + \phi_0 - \frac f{f_s} (n-1)
 * - \phi_0\right)}\right)\\
 *  & = \mathrm{arg}\left( A^2 e^{j2\pi\left( \frac f{f_s} n - \frac f{f_s}
 * (n-1)\right)}\right)\\
 *  & = \mathrm{arg}\left( A^2 e^{j2\pi\left( \frac f{f_s}
 * \left(n-(n-1)\right)\right)}\right)\\
 *  & = \mathrm{arg}\left( A^2 e^{j2\pi \frac f{f_s}}\right) \intertext{$A$ is real, so is
 * $A^2$ and hence only \textit{scales}, therefore $\mathrm{arg}(\cdot)$ is invariant:} &=
 * \mathrm{arg}\left(e^{j2\pi \frac f{f_s}}\right)\\
 *  &= \frac f{f_s}\\
 *  &&\blacksquare
 * \f}
 */
class ANALOG_API quadrature_demod_cf : virtual public sync_block
{
public:
    // gr::analog::quadrature_demod_cf::sptr
    typedef std::shared_ptr<quadrature_demod_cf> sptr;
 
    /* \brief Make a quadrature demodulator block.
     *
     * \param gain Gain setting to adjust the output amplitude. Set
     *             based on converting the phase difference between
     *             samples to a nominal output value.
     */
    static sptr make(float gain);
 
    virtual void set_gain(float gain) = 0;
    virtual float gain() const = 0;
};
 
} /* namespace analog */
} /* namespace gr */
 
#endif /* INCLUDED_ANALOG_QUADRATURE_DEMOD_CF_H */