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/* -*- 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 boost::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 */
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