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ADC12DJ3200: Accuarcy of SYSREF Frequency for ADC12DJ3200 in Multiple ADC synchronization

bharath
Intellectual 425 points
Part Number: ADC12DJ3200
Other Parts Discussed in Thread: LMX2582, LMK04828,

Dear sir,

We are using 2 nos of ADC12DJ3200 for our requirement where multiple ADC synchronization is required.

Stage 1 :

Operating the two ADC's at device clock of 3.2GHz in which maximum SYSREF frequency of 10MHz as per equation 2 in datasheet.

Which is able to generate from LMK04828B PLL and Device clock of 3.2GHz  from LMX2582 RF PLL.

Stage 2 :

If device clock of 1.35GHz and require SYSREF frequency to be 4.21875MHz (max)

But we are unable to generate these  frequency from LMK04828.

These are frequency & divider settings for SYSREF in LMK04828 PLL.

VCO Frequency : 3000MHz

SYSREF Divider Value : 711

SYSREF output Frequency : 4.219409MHz

There is frequency offset of 65.9KHz. 

Query : 

1. Whether these frequency offset is acceptable for multiple ADC synchronization.

2. What will be impact of synchronization over temperature range with this frequency offset.

Regards,

Jaya Bharath Reddy K

  • 0
    TI__Mastermind 44680 points

    Hi Bharath

    The SYSREF frequency must be the exact calculated value of the LMFC frequency, or any sub-harmonic of that frequency. Any frequency offset from the desired value will result in an unstable or non-operative JESD204B link.

    Are you using the ADC12DJ3200EVM, or a board of your own design?

    If it is your own design can you share a detailed block diagram showing the clocking architecture and connections between the LMK04828, LMX2582 and ADC12DJ3200 devices?

    Unfortunately due to VCO limitations the LMK04828 cannot directly create 1.35 GHz or multiples of that frequency. On the ADC12DJ3200EVM we use the LMX2582 to create the high frequency clock for the ADC, and also an input clock for the LMK04828. This input clock to the LMK04828 is used with clock distribution mode to create the needed FPGA DEVCLK and system SYSREF frequencies. This combination gives greater frequency flexibility than using the internal VCOs of the LMK04828. A similar approach might be possible in your system.

    Best regards,

    Jim B