Xilinx FFT ipcore with ADC question

[abort]

xilinx fft core spectrum

I have audio data coming out of an ADC.

I wanted to use a Xilinx FPGA to run it through a FFT and I noticed that Xilinx has a FFT ipcore available in their CORE Generator that I believe I can use. The input requires a real part and an imaginary part, but I only have the real part [the data coming off the ADC].

I read "Distributed Half Band Filter (DHBF) provides an efficient mechanism for converting a digitised signal from an ADC into a complex representation for input to the FFT transform." and "The ADC output is first applied to a DHBF (Distributed Halfband Filter), which converts the real input signal to a complex output at half the rate."

So my question is does Xilinx also provide a DHBF ipcore through CORE Generator or how would I otherwise go about getting a DHBF to put between the ADC and the FFT?

Thank you very much.

 

[muralicrl]

fft bitwidth growth

Hi Friend,

You can apply Hilbert transform to the output of ADC, so that you will get both I and Q samples which can be directly given to FFT core which requires both I and Q samples.

For more details kindly contact me.

regards,
N.Muralidhara
MSRS, CRL-BEL

 

[abort]

xilinx fft audio

I appreciate your response about the Hilbert Transform!

When I select that in the Xilinx CORE generator and build it, it gives me the I and Q parts, as you mentioned, the I part is 16 bits [the length of the input], but the Q part is 35 bits. I'm not sure why. It seems, however, that I am able to adjust the output width of Q somewhat based on what I used for the Coefficient Width when creating the Hilbert Transform [down to a minimum of 21 bits]. The Q width is always at least 5 bits wider than the I width.

I did find this in the Xilinx documentation as to why the I and Q outputs are of different size:

Filter input data is supplied on the DIN port (N bits wide) and filter output samples are presented on the DOUT port (R bits wide). The output width R is the sum of the data bit width N, the coefficient bit width K, and the bit growth due to the number of coefficients. ... For Hilbert transform filter implementations, a pair of In-Phase/Quadrature data outputs is provided. The In-Phase data output is N bits wide, as it is a delayed version of the input data, while the Quadrature data output is R bits wide, calculated as described previously.

But the FFT that I created in CORE generator is expecting the I and Q parts to be 16 bits wide each.

What am I missing? Thank you very much!

 

[chris_xieq]

fft core xilinx

Hi Abort,

Have you ever sove the problems, I meen the problem too, audio comes from ADC, I need to analyzer the THD/Spectrum through FFT, I want to use Xilinx's Core too.

Hi muralicrl,

As mentioned above, could you kindly give me some advise please? Thanks.

Regares,

Chris.

 

[liupardon]

adc xilinx

hi,abort & chris_xieq

i meet the same question too. sample data from ADC , then i need to calculate the spectrum through FFT. i just want to know that the IPcore does work ok?

 

[kavitha_bonthu]

xilinx adc

Hello............
You can compute the FFt of a real signal by giving imaginary part to be zero..........
So for xilinx FFT core you can just give the ADC o/p to real input and make Imaginary input to be always zero........
Hope you get my point........