Re: [oc] New! FFT core, transform gain issue

["Saumil Merchant" <msaumil@hotmail.com>]

Hi,
Could you pls send your testbench.

Saumil

----- Original Message -----
From: <h.larsen@risoe.dk>
To: <cores@opencores.org>
Sent: Tuesday, November 19, 2002 10:56 AM
Subject: [oc] New! FFT core, transform gain issue


> Hi,
>
> I have tested the cfft core, but found that the gain is 29.4 both in
N=1024
> FFT and IFFT, whereas the documentation says it should be 0.0287 in FFT
> mode, and 29.4 in IFFT mode.
>
> I simply supply a real ampliude of a sine wave to the input of the
> cfft1024X12: Something like->
> Iin=A*sin(2pi*F*t) + DC;
> Qin=0;
>
> and measure the output amplitude (FFT or IFFT, no difference, except to
> phase of output). It gives a peak at bin 0 of DC*29.4 and two peaks at the
> proper bins with an amplitude of 14.7*A each, which makes sense only if
the
> gain is 29.4=14.7*2 (two bins).
>
> Anybody who have tried similar things?
>
> In particular a comment from the briliant designer ZHAO Ming would be very
> welcome.
>
> regards
> henning larsen
> Electronics des. engineer
> Risoe national laboratory
> Denmark
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