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interfacing CDCLVD1208 to CDCE72010

David Burton
Expert 1330 points
Other Parts Discussed in Thread: CDCE72010, CDCLVD1208

Hi,

I'm driving a CDCE72010 VCXO input with a DC coupled CDCLVD1208.  I have placed an external 100 ohm termination, but it's location in the layout is not ideal.  The route is about 1/2" long with the terminator closer to the source.

Would I be better off to use internal terminations in the CDCE72010?  From the diagrams it looks like that also requires the internal bias to be on and connected.  Can I drive the bias connected internal terminations with the CDCLVDS1208 DC coupled?

Some LVDS output typical circuits show common mode being set by pretty high resistances (~10k).  It seems if that is so the load internal termination bias would be able to work with that.

Thanks,

David B

  • 0
    TI__Expert 4150 points

    David,

    yes, you should probably remove the external resistor and use internal biasing instead. The CDCLVD1208 is ok to driving the CDCE72010 with internal biasing being enabled.

    Best regards. Falk Alicke

  • 0 in reply to Fritz
    Expert 1330 points

    Since it doesn't seem possible to use the internal termination without internal bias does that mean I also need to AC couple the CDCLVD1208 to use internal termination?  Or is the 1208 bias network sufficiently high impedance to ride it out?

    What is that INV switch for anyway?  Doesn't seem much use in series with the N switch.

  • 0 in reply to David Burton
    Expert 1330 points

    I placed a little snip of the internal circuit from page 49 but it doesn't show up after posting.  Do I have to post snips as files to get them in?  How did you do it?

     

    Thanks.

  • 0 in reply to David Burton
    TI__Expert 4150 points

    you can leave the internal biasing enabled and DC coupled, no problem (just make sure it's set to LVDS, not LVPECL if you drive from CDCLVD1208).

    I attached the snips as "INSERT IMAGE" - a button on the editor next to the "INSERT FILE" button. I don't think copy/paste works otherwise.

  • 0 in reply to Fritz
    Expert 1330 points

    OK, Thanks.

    Note my email notice did show the snip, it's just not visible here on the forum.  I'll use the insert image, though that does mean I need to save the snip to a file first..