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AFE7900: Sampling frequency query

ArTzy
Genius 13959 points
Part Number: AFE7900

Hi Experts,

Seeking your assistance on this query from customer:

[1] How to sampling the central frequency using the AFE7900 board? I have tried to sample a central frequency at 1.6G, but there is no anything on your software.

[2] How to test central frequency using AFE7900? Can you give me some introduction or another document?

Thank you very much.

Regards,
Archie A.

  • 0
    TI__Genius 10505 points

    Hi Archie,

    Band center frequency of RX/ADC input signal is set by NCO frequency of RX chain. In default scripts of AFE79xx EVM software are set by below parameters:

    sysParams.rxNco0		= 	[[5400,5400],			#Band0, Band1 for RXA 
							[500,500],        		#Band0, Band1 for RXB 
							[2500,2500],        	#Band0, Band1 for RXC 
							[1800,1800]]        	#Band0, Band1 for RXD

    If customer needs to change this to 1600 MHz, these can be updated to 1600. All systemParamters used in software are defined in "AFE79xx_ConfigurationGuide_SBAA417_Jun2020.pdf" document. This can be accessed in AFE79xx secure folder (www.ti.com/mysecuresoftware)

    Please note that 1600MHz is close to Nyquist boundary when using ~3GSPS ADC sample rate. Sample rate has to be frequency planned if band of interest is close to Nyquist boundary. 

    Regards,

    Vijay

  • 0 in reply to Vijayendra Varma Siddamsetty
    TI__Genius 13959 points

    Thank you, Vijay.

    We have some questions,

    1. Is the Transmission center frequency tolerance and Freq offset the same parameter?

    2. Is the Transmit symbol clock frequency tolerance and Symbol Clk Err the same parameter? How are they defined?

    3. May I ask how the Transmit symbol clock frequency tolerance is calculated?

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Genius 10505 points

    Hi Archie,

    1. Transmit chain (TX) center frequency is set by 'sysParams.txNco' parameter. Baseband sample rate can be calculated by from TX sample rate (sysParams.Fdac) and interpolation factor (sysParams.ducFactorTx). Baseband sample rate = Fdac/ducFactorTx (DUC pass band is ~80% of baseband rate)

    2. Symbol clock frequency and Clk Err are specific to type of modulation scheme used. 

    3. Transmit symbol clock frequency tolerance is also specific to type of modulation scheme used. These are not AFE config parameters. 

    Regards,

    Vijay

  • 0 in reply to Vijayendra Varma Siddamsetty
    TI__Genius 10505 points

    Hi Archie,

    Adding to my previous response...

    The NCO frequency resolution is 32-bits, which translates to an maximum frequency error of 0.1 parts per billion relative to the input clock.

    Regards,

    Vijay