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Subversion Repositories iqcorrection
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Rev 2 → Rev 3
/trunk/Generate_Normal_Distribution_Random_Noise.vhd
0,0 → 1,64
library ieee; |
use ieee.std_logic_1164.all; |
use ieee.math_real.all; |
use ieee.numeric_std.all; |
use work.random_int.all; |
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--by MEP 22 February 2011 |
--usage: |
--this is a function, which means it can be on the right-hand side |
--of an assignment. It returns a mean-zero random number from a |
--normal distribution. The argument is a real number that indicates |
--the standard deviation desired. |
-- |
--random_noise(sigma); |
-- |
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package normal_distribution_random_noise is |
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function random_noise ( |
sigma : real) |
return real; |
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end package normal_distribution_random_noise; |
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package body normal_distribution_random_noise is |
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function random_noise ( |
sigma : real |
) |
return real is |
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--variables |
variable u_noise: real; --uniform distribution noise |
variable n_noise: real := 0.0; --normal distribution noise |
variable seed1 : positive; |
variable seed2 : positive; |
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begin |
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--obtain a uniformly distributed random number |
uniform(seed1, seed2, u_noise); |
--report "Random uniform noise is " & real'image(u_noise) & "."; |
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for normal_count in 0 to 12 loop |
--Turn the uniform distributed number |
--into a normally distributed number |
--by using the central limit theorem. |
--Make it mean zero and make it have |
--the range of the uniform numbers |
--that it is composed from. |
n_noise := n_noise + u_noise; |
end loop; |
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n_noise := n_noise - (0.5)*(real(12)); --normal distribution with a mean of zero |
--report "Random normal noise is " & real'image(n_noise) & "."; |
n_noise := n_noise/(real(12)); |
--report "Random normal noise using range of uniform is " & real'image(n_noise) & "."; |
n_noise := sigma*n_noise; |
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return n_noise; |
end function random_noise; |
end package body normal_distribution_random_noise; |
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