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added Fs/4 complex down conversion

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Ahmet Inan 2019-04-03 20:53:17 +02:00
commit cd7d55a2c4
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4
README.md
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@ -56,6 +56,10 @@ Normalizers for [periodic](https://en.wikipedia.org/wiki/Periodic_function) sign
[Numerically controlled oscillator](https://en.wikipedia.org/wiki/Numerically_controlled_oscillator) implemented using a [phasor](https://en.wikipedia.org/wiki/Phasor) and [complex multiplication](https://en.wikipedia.org/wiki/Complex_number#Multiplication) instead of a [lookup table](https://en.wikipedia.org/wiki/Lookup_table).
### [cdc.hh](cdc.hh)
Fs/4 [Complex down conversion](https://en.wikipedia.org/wiki/Digital_down_converter)
### [fmd.hh](fmd.hh)
[Frequency modulation](https://en.wikipedia.org/wiki/Frequency_modulation) [demodulation](https://en.wikipedia.org/wiki/Demodulation) with and without [atan2](https://en.wikipedia.org/wiki/Atan2).

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cdc.hh Normal file
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@ -0,0 +1,51 @@
/*
Fs/4 Complex down conversion
Copyright 2019 Ahmet Inan <inan@aicodix.de>
*/
#pragma once
#include "filter.hh"
#include "window.hh"
namespace DSP {
template <typename TYPE, int TAPS>
class CDC
{
typedef TYPE complex_type;
typedef typename TYPE::value_type value_type;
value_type real[(TAPS-1)/4];
value_type imag[(TAPS-1)/2];
value_type imco[(TAPS-1)/4];
value_type reco;
bool sign;
public:
CDC(value_type a = value_type(2)) : sign(false)
{
Kaiser<value_type> win(a);
LowPass2<value_type> hbf(1, 4);
reco = win((TAPS-1)/2, TAPS) * hbf((TAPS-1)/2, TAPS);
for (int i = 0; i < (TAPS-1)/4; ++i)
imco[i] = win(2*i+(TAPS-1)/2+1, TAPS) * hbf(2*i+(TAPS-1)/2+1, TAPS);
}
complex_type operator()(value_type in0, value_type in1)
{
sign = !sign;
value_type re = reco * real[0];
for (int i = 0; i < (TAPS-1)/4-1; ++i)
real[i] = real[i+1];
real[(TAPS-1)/4-1] = sign ? in1 : -in1;
for (int i = 0; i < (TAPS-1)/2-1; ++i)
imag[i] = imag[i+1];
imag[(TAPS-1)/2-1] = sign ? in0 : -in0;
value_type im = imco[0] * (imag[(TAPS-1)/4-1] + imag[(TAPS-1)/4]);
for (int i = 1; i < (TAPS-1)/4; ++i)
im += imco[i] * (imag[(TAPS-1)/4-1-i] + imag[(TAPS-1)/4+i]);
return complex_type(re, im);
}
};
}