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Participant abitofmaya
Participant
361 Views
Registered: ‎08-27-2018

Incorrect IFFT output

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I am trying to implement IFFT after FFT. The FFT output in simulation is correct. I then tried to do an IFFT of the output which is incorrect. Both the FFT and IFFT is cnfigured for unscaled output  in natural order. It is just an 8 point computation. Can anyone tell what I may be missing?

2019-01-14 20_16_01-.png
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1 Solution

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Participant abitofmaya
Participant
256 Views
Registered: ‎08-27-2018

Re: Incorrect IFFT output

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I have finally found the solution. The output of the FFT must be scaled by a factor of 1/N before it is applied to the input of the IFFT. This can be done either by setting the scaling schedule or by shifting the output of the FFT if unscaled option is used.

3 Replies
Explorer
Explorer
323 Views
Registered: ‎05-21-2015

Re: Incorrect IFFT output

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@abitofmaya,

I'm sorry but ... I can't read your FFT trace to see or know what's going on.

Therefore, just guessing, I'm wondering if the trace isn't long enough.  The delay necessary through the IFFT should be roughly the same as the necessary delay though the FFT in the first place.

Dan

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Participant abitofmaya
Participant
299 Views
Registered: ‎08-27-2018

Re: Incorrect IFFT output

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@dgisselq,
Since the FFT output was correct, I removed that part and I used the FFT output as input to the IFFT part. Anyway, I have attached both the FFT and IFFT simulation screenshots below. It seems like it again computes FFT and provides output in bit/digit reversed order.

2019-01-15 10_51_35-Wave.png
2019-01-15 10_51_53-Wave.png
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Participant abitofmaya
Participant
257 Views
Registered: ‎08-27-2018

Re: Incorrect IFFT output

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I have finally found the solution. The output of the FFT must be scaled by a factor of 1/N before it is applied to the input of the IFFT. This can be done either by setting the scaling schedule or by shifting the output of the FFT if unscaled option is used.