AD9515 IBIS model not complete

Hello everyone,

I am analyzing on CST signal integrity of an AC coupled 250MHz clock from the AD9515's LVPECL output with the IBIS model available on the net.

Unfortunately this model is not complete so I don't understand why this was provided ? I have only LVDS output but no LVPECL.


May there be something I am missing in IBIS model configuration ?

Thanks in advance

  • Hi Rleduc,

    Thanks for reaching out. 

    I'm Rolynd, a product applications engineer from ADI.

    Regarding your concern about the AD9515 IBIS model, there is an LVPECL model present. Upon checking, it is in pins 22 and 23, with the model name "pecl_clk."

    I don't have CST installed on my computer, and I have not used it before, so I can't precisely tell why the LVPECL model did not appear on your end. But I have tested the model on Keysight ADS 2022, and it seems to be working fine. Looking through the LVPECL model, it has a Model_type "Output_ECL." If there is a differential "Output_ECL" IBIS block on CST, I think you should use it for the LVPECL model to appear on the model list.

    I hope this helps. Let me know if you need further assistance.

    Regards,
    Rolynd

  • Hello Rolynd, thanks for answering.

    That is reassuring to see that you could find lvpecl model in the IBIS model, and so did I. In deed I could notice that the "Output_ECL" type is not automatically recognized by CST, so I need to find a workaround as you told me.
    However, I saw that ECL driver end technology is an emitter follower technology, that should be provided a pull down resistor otherwise there is no path for falling edge current. So it is not clear to me that IBIS provides a rising/falling curve that is already working well "on die", while it all depends on this pulldown resistor !

    Best regards

    Roman

  • Hi Roman,

    You could contact a CST support representative to help you find a workaround on simulating the Output_ECL model type.

    As for the Output ECL IBIS model, it is different from a totem-pole output structure. When the model is categorized as an Output_ECL, the simulator makes assumptions different from a typical totem-pole output configuration, including the pulldown component of the model. A good discussion on ECL IBIS modeling can be read here: https://ibis.org/birds/bird1.txt.

    Regards,
    Rolynd