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Altera_Forum

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03-01-2013
03:30 AM

665 Views

why fft core's output is conjugate

Dear all,

When I using quartu12.0's fft megacore IP, I found such problems: chose variable streaming and natural order for both input and output order, set ifft, make sink real = impulse, sink_imag =0, 1024 point, the ifft output from the simulation shows that the (source_real + 1j*soure_imag) is the conjugate of the ideal result from matlab. Please help me. Thank you very much. And the result is caputured as follows: https://www.alteraforum.com/forum/attachment.php?attachmentid=6874
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Altera_Forum

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03-01-2013
12:32 PM

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It could be your understanding of ofrequency sense is wrong between matlab model and ifft core.

You got cos waveform on real ifft output and -sin waveform on imag ifft output. This means your so called impulse is one nonzero sample at a negative frequency location i.e. after midpoint of 1024 (well further from sample 512) . So in which sample did you put that impulse?For more complete information about compiler optimizations, see our Optimization Notice.