GNU Radio Manual and C++ API Reference 3.7.14.0
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quadrature_demod_cf.h
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1/* -*- c++ -*- */
2/*
3 * Copyright 2004,2012 Free Software Foundation, Inc.
4 *
5 * This file is part of GNU Radio
6 *
7 * GNU Radio is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 3, or (at your option)
10 * any later version.
11 *
12 * GNU Radio is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 *
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18 * along with GNU Radio; see the file COPYING. If not, write to
19 * the Free Software Foundation, Inc., 51 Franklin Street,
20 * Boston, MA 02110-1301, USA.
21 */
22
23#ifndef INCLUDED_ANALOG_QUADRATURE_DEMOD_CF_H
24#define INCLUDED_ANALOG_QUADRATURE_DEMOD_CF_H
25
26#include <gnuradio/analog/api.h>
27#include <gnuradio/sync_block.h>
28
29namespace gr {
30namespace analog {
31
32/*!
33 * \brief quadrature demodulator: complex in, float out
34 * \ingroup modulators_blk
35 *
36 * \details
37 * This can be used to demod FM, FSK, GMSK, etc. The input is complex
38 * baseband, output is the signal frequency in relation to the sample
39 * rated, multiplied with the gain.
40 *
41 * Mathematically, this block calculates the product of the one-sample
42 * delayed input and the conjugate undelayed signal, and then calculates
43 * the argument of the resulting complex number:
44 *
45 * \f$y[n] = \mathrm{arg}\left(x[n] \, \bar x [n-1]\right)\f$.
46 *
47 * Let \f$x\f$ be a complex sinusoid with amplitude \f$A>0\f$, (absolute)
48 * frequency \f$f\in\mathbb R\f$ and phase \f$\phi_0\in[0;2\pi]\f$ sampled at
49 * \f$f_s>0\f$ so, without loss of generality,
50 *
51 * \f$x[n]= A e^{j2\pi( \frac f{f_s} n + \phi_0)}\f$
52 *
53 * then
54 *
55 * \f{align*}{ y[n] &= \mathrm{arg}\left(A e^{j2\pi\left( \frac f{f_s} n + \phi_0\right)}
56 * \overline{A e^{j2\pi( \frac f{f_s} (n-1) + \phi_0)}}\right)\\
57 * & = \mathrm{arg}\left(A^2 e^{j2\pi\left( \frac f{f_s} n + \phi_0\right)} e^{-j2\pi(
58 * \frac f{f_s} (n-1) + \phi_0)}\right)\\
59 * & = \mathrm{arg}\left( A^2 e^{j2\pi\left( \frac f{f_s} n + \phi_0 - \frac f{f_s} (n-1)
60 * - \phi_0\right)}\right)\\
61 * & = \mathrm{arg}\left( A^2 e^{j2\pi\left( \frac f{f_s} n - \frac f{f_s}
62 * (n-1)\right)}\right)\\
63 * & = \mathrm{arg}\left( A^2 e^{j2\pi\left( \frac f{f_s}
64 * \left(n-(n-1)\right)\right)}\right)\\
65 * & = \mathrm{arg}\left( A^2 e^{j2\pi \frac f{f_s}}\right) \intertext{$A$ is real, so is
66 * $A^2$ and hence only \textit{scales}, therefore $\mathrm{arg}(\cdot)$ is invariant:} &=
67 * \mathrm{arg}\left(e^{j2\pi \frac f{f_s}}\right)\\
68 * &= \frac f{f_s}\\
69 * &&\blacksquare
70 * \f}
71 */
73{
74public:
75 // gr::analog::quadrature_demod_cf::sptr
76 typedef boost::shared_ptr<quadrature_demod_cf> sptr;
77
78 /* \brief Make a quadrature demodulator block.
79 *
80 * \param gain Gain setting to adjust the output amplitude. Set
81 * based on converting the phase difference between
82 * samples to a nominal output value.
83 */
84 static sptr make(float gain);
85
86 virtual void set_gain(float gain) = 0;
87 virtual float gain() const = 0;
88};
89
90} /* namespace analog */
91} /* namespace gr */
92
93#endif /* INCLUDED_ANALOG_QUADRATURE_DEMOD_CF_H */
quadrature demodulator: complex in, float out
Definition: quadrature_demod_cf.h:73
boost::shared_ptr< quadrature_demod_cf > sptr
Definition: quadrature_demod_cf.h:76
static sptr make(float gain)
virtual void set_gain(float gain)=0
virtual float gain() const =0
synchronous 1:1 input to output with history
Definition: sync_block.h:38
#define ANALOG_API
Definition: gr-analog/include/gnuradio/analog/api.h:30
Include this header to use the message passing features.
Definition: basic_block.h:45