ADRV9026: Sysref Calculation Confusion

Hi All,

I am seeing two different formula for calculating sysref. I don't which one is correct and why ? Please help.

fs =  245.76 MHz, K = 32, S = 1

Case 1:

jesd_frame_clk  =  fs / K  = > 245.76 MHz/ 32 = 7.68 MHz

LMFC =  jesd_frame_clk/ S. =>  7.68 / 1 = > 7.68 MHz

SYSREF  =  LMFC /N where N = 1 so sysref = 7.68 MHz / 1  = > 7.68 MHz

Case 2:

SYSREF = fs / LCM ( 64, S*K)  = > 245.76 / LCM ( 64, 1*32) = > 245.76/64 = >  3.84 MHz

A) Which formula holds true ? 

B) Why should we have 64 in LCM ? How does this magic number come ? Is this an optimum number for proper wait clock period b/w each sysref and Is it applicable only for gapped and periodic sysref  but not for single shot ?

Regards,

Manish

 

Top Replies

    •  Analog Employees 
    Jun 21, 2021 +1 verified
    A) Which formula holds true ? 

    For ADI Transceiver we follow case 1. Please refer to the below reference from JESD standard

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