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Altera_Forum
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16 years ago

Altera FFT - output scaling. How to do this correctly?

Hi, I do not get correct scaled results if I do everything the FFT user guide recommends. I have instantiated a 1024 points FFT, with single output and burst architecture. The data width...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
16 years ago

A further note on shifting:

imagine your data is 15bits

if data = Ox00ff (255)

shift 4 bits towards sign bit to become Ox0ff0 (or Ox0ff&four internal bits if available). = 4080 = 16 x 255

or shift 4 bits towards LSB to become Ox000f = 15 =~ 255/16

if your data = Ox7FFF (your example) = -1

shift 4 bits towards sign bit to get Ox7FF0 = -16

or 4 bits towards LSB to get Ox7FFF = -1 (this is the odd case, woudn't divide)