Level of noise in fft

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Maxime Duquesnoy
Maxime Duquesnoy 2016 年 6 月 10 日
コメント済み: Maxime Duquesnoy 2016 年 6 月 10 日
Hello everyone,
I am trying to model a DAC , to do so I need to write a Zero Order Hold function , which repeats each sample a certain number of times. I see that the spectrum has not the same amplitude before and after ZOH . I used a number of points in power of 2 so that I can see the noise floor.
I have really big problems to make the noise appear at the same level than before. I join 2 photos, 1 which is the result of a 3bit DAC on a 100 Hz sine wave and then the spectrum of the holded signal.
Could you tell me why the noise level becomes 0 dBm when it was -78 dBm before ZOH ?
I also give you my ZOH code;
L=length(signal);
output_signal=[];
for j=1:L;
x=duration;
while x>0
output_signal=[output_signal signal(j)];
x=x-1;
end;
end;
Thank you for your help.

採用された回答

J. Webster
J. Webster 2016 年 6 月 10 日
This looks like you aren't windowing your data properly before you take the fft of it. Try applying a Hamming or Hanning window first.
  2 件のコメント
Maxime Duquesnoy
Maxime Duquesnoy 2016 年 6 月 10 日
I solved my problem when I was taking my shower. For the first one, I used the power per sample, for the second I forgot to divide by the signal's length. Lesson: do never forget what you put in the functions you create Thank you for your help. Regards

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