AnsweredAssumed Answered

vrf Problems with fft analysis

Question asked by VRFuser on Dec 23, 1999
Hello,

I'm have a problem with the fft-function. via a logic analyzer, I collect 4096 samples of
a 9.765625kHz sinus, sampled at 10MHz, so 1 period = 1024 samples.
>From those 4096 samples, I use 1024 of them (so 1 period) as an input for the
fft-function. With the result of the fft, I calculate the SINAD.

Now the problem : The SINAD is influenced by the starting point of the 1024
samples, i.e. the phase of the sinus when the sampled data is AD-converted.
The SINAD is maximum when the first sample is the positive maximum of the
sinus-function.

I tought that when I have 1 period at the input of the fft, the result isn't dependant
of the starting phase.

Am I wrong? If so please tell me.
If not,  is there a problem with the fft-function.


Everybody, Merry Christmas and a Happy Newyear.

Thanks in advance,

Wouter Dejaeghere
Test Department
Siemens BCB
Oostkamp-Belgium
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