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CDCLVC1102 VDD SUPPLY

Mark McPhail
Prodigy 40 points
Other Parts Discussed in Thread: CDCLVC1102

HI,

I'm using a CDCLVC1102 clock buffer in my design and am looking for advice on how to filter/decouple the VDD input.  I'm feeding the CLKIN pin with a 20MHz signal from an OCXO.  Should I use a common, filtered supply for both or power each using a separate, filtered supply.

3.3V---->filter---->OCXO

            -->filter---->CDC

or

3.3V----->filter------>OCXO

                           ------->CDC

thanks,
Mark

 

  • 0
    TI__Expert 4150 points

    Hello Mark,

    It depends a little on your overall system requirements concerning noise. As with any CMOS buffer the current is switched unbalanced, which means you want to add some decoupling cap to the device supply. The OCXO and CDCLVC1102 switching frequency are the same, which itself is good for you don't get spurs at other frequency ranges. However, the actual switching time is somewhat offset depending on the CDCLVC1102 input-to-output delay, which means some amplitude modulation can occur through the supply. 

    The savest design approach is to filter both power supplies but I suspect your OCXO itself doesn't cause much switching noise, so it's probably ok to run both devices from the same supply. I suggest however to add sufficient AC coupling caps to the VCC input of each device.

     

    Best regards, Fritz