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Altera_Forum
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16 years ago

White Noise Spectrum

I have use a simple LFSR to generare random number to generate white noise. Set of random number are pass through to FFT(power in db vs freq). However, the freq response is increasing at low freq. Th...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
16 years ago

Moin,

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hi WK, i have different set of length of LFSR. However, the spectrum doesn't change.

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What are the different lengths? Are you sure, that the feedback is in a way, that the repetition rate gets minimal for each length?

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Is this a problem or normal when using the LFSR to generate random number?

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This is higly depending on your application. Consider e.g. a LFSR with 8 bit length, which you'll use to obtain an 8 bit random number with each clk. Then the prediction of the next number based on the current number is pretty easy with a probability of 50% - that's of course a very bad random generator. But if you perform more clk cycles between sampling random numbers and you increase the length of the LFSR, quality of your random numbers will increase too. So it depends on your requirements of the random numbers, at which length the Generator will be sufficient. But of course it will never be a "real" random, regardless of the length.

cheers,

WK