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FFT in BF506

Question asked by f.amato@gatech.edu on Feb 24, 2015
Latest reply on Apr 6, 2015 by f.amato@gatech.edu

Hello all,

I need help  to compute (or define) the ADC sampling frequency.

 

I am using CCES and BF506 EZ-kit to sample I and Q data and apply FFT.


I am now testing the code I wrote by injecting a sin wave of 1 MHz.

the ADC is sampling the signal and the FFT (rfftf_fr16()) on 512 points is giving a reasonable spectrum.

 

Nevertheless, the spectrum doesn't seem to give a correct info about the signal frequency.
I think I am misunderstanding the values of the sampling frequency of the ADC.

 

In the CCES example project (AD7266_and_ACM), the initial variables are defined as follow:

 

#define ACM_DEV_NUM    0

#define SPORT_DEV_NUM  1

 

 

#define ACLK         5000000u

 

 

#define MHZTOHZ       (1000000)

#define CLKIN         (25 * MHZTOHZ)

#define CORE_MAX      (400 * MHZTOHZ)

#define SYSTEM_MAX    (100 * MHZTOHZ)

#define VCO_MIN       (72 * MHZTOHZ)

 

 

#define NUM_ACM_EVENTS  6

#define TIME_PER_EVENT  350

#define START_TIME      100

 

 

#define GP_TIMER  2

#define PERIOD    (START_TIME + NUM_ACM_EVENTS*TIME_PER_EVENT)

#define WIDTH     10

 

 

is the ADC sampling rage of 5 MHz?
Is it defined as SCLK/Period? (with SCLK = 100 MHz in this case)?

 

thanks a lot for your help!

 

Francesco

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