AD9629 input clock design

Hi,

I have got a working design with 4 ADCs (AD9629), they have for each an input clock design just like the picture attached.

(I would like to keep 4 times AD9629 for versatility...)

All of my ADC are synchonized to the same clock at 5Mghz.

My question are:

- Is there enough (current/power) for powering 4 Adcs with a single clock differential input?

- Is there any precautions I need to implement?

thanks in advance.

  • 0
    •  Analog Employees 
    on Feb 25, 2020 3:17 PM

    Hi CrazyFrog,

    Thanks for using the AD9629.

    • You do not mention what is driving the clock in your current system. What is the drive capability and/or power output of your clock source?
    • You said that each ADC has the same clock circuit as shown in your diagram. Is the same clock source driving all four of these, or does each one have its own clock source?
    • For clarification, in your new system, are you proposing to use one transformer to drive all four ADCs?

    Thank you.

    Doug

  • Thanks you for answering:

    My answers just below

    - Yes, the ADCCLKIN is an output of a microcontroller, it can output few ma, i guess.

    - On my current design, yes each ADC has its own clock source ( one PWB-1-BLC per ADC)

    - Yes i would like to use just one transformer for driving all four ADCs.

    Regards

  • 0
    •  Analog Employees 
    on Feb 26, 2020 5:46 PM in reply to crazyfrog

    Hi CrazyFrog,

    Thank you for your reply. I'm still not clear on one detail. In your present system, is there one clock source (one microcontroller output) driving the four transformers, or is each transformer driven by a different microcontroller output?

    Thank you.

    Doug

  • Yes there is only one gpio output pin ( of the microcontroller) driving the four clock system (see the picture attached)

    Thanks you

  • 0
    •  Analog Employees 
    on Feb 27, 2020 5:59 PM in reply to crazyfrog

    Hi CrazyFrog,

    From a drive strength perspective, it seems to me that your single microcontroller output will have to supply about the same amount of drive power to one transformer that fans out to 4 loads, as it does driving four transformers each driving one clock load.

    So, from a drive strength perspective I think you are OK.

    Try to keep your clock signal path as short as possible to reduce the transmission line effects.

    If there is an output impedance associated with your clock driver pin, you might want to add pads for a possible matching termination resistor, right before the transformer.

    Thanks,

    Doug