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duke4055

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03-04-2020 04:34 AM

464 Views

Registered:
01-31-2018

FFT IP spectral leakage

Hello,

i have a question about Xilinx FFT IP.

I use xilinx multiplier IP & FFT IP as below.

Multiplier(complex signal i, q data*fft windowing coefficients(2048)) IP >>>>>>> FFT IP

the output of 2 multipliers(each complex i * fft windowing coefficients(2048) & complex q * fft windowing coefficients)) goes into input of xilinx FFT IP. the operating clock of multipliers & FFT IP is same as 15.36MHz.

When the frequency of complex data is 0Hz, the result of fft is good. But, when it is 4 or 5 Mhz, fft output appears spectral leakage of FFT.

How could i solve this problem??

please help me.

1 Reply

archangel-lightworks

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03-04-2020 05:07 AM

451 Views

Registered:
07-23-2019

After a product of signals you get the sum and difference of frequencies. typically the sum is discarded by low-passing after the product. If you feed an FFT with that, if the HF component is above the Nyquist frequency it will appear aliased in your spectrum.

Also bear in mind that multipliers normally take more than one cycle, let's say 4, in that case your maximum data rate would be 15 MHz/4 = 3.75 MHz, anything above you'd be screwing it up (dropping points to be precise). For a multiplier to produce data at 15 MHz, you may need to clock it faster.