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Steve9's avatar
Steve9
Icon for Occasional Contributor rankOccasional Contributor
6 months ago
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Agilex 7 F/I Series True Differential Input Termination

Hi,  The Agilex F/I Series GPIO User Guide indicates that if using AC coupling for the true differential inputs you should add external voltage bias circuitry and has no examples of AC coupling with...
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  • FvM's avatar
    FvM
    6 months ago

    Hi Steve,

    reviewing documents and reference design, I agree that GPIO manual, datasheet and development kit schematic are inconsistent in several regards. Looking also at IBIS file, there seems to be a non-linear pull-up feature for TDS input standard which effectively pulls Vicm to about half supply with applied signal. Not sure if IBIS input characteristic is real or roughly simplified.

    So all-in-all, it seems like development kit implementation is a possible minimal effort termination option.

    Regards
    Frank

FvM's avatar
FvM
Icon for Super Contributor rankSuper Contributor
6 months ago

Hi,

don't agree with your conclusions. There are no indications of internal bias circuit. Datasheet just specifies required voltage levels without mentioning how they are achieved. It's identical to other parts specification that surely miss internal bias. Didn't yet check mentioned dev kit schematic.

Steve9's avatar
Steve9
Icon for Occasional Contributor rankOccasional Contributor
6 months ago

Ok thanks, I agree datasheet doesn't indicate internal bias. I was basing my comments about internal bias based on the IBIS model seeming to have an internal Bias when the tds12_inp input buffer model is used for the Agilex. But that may just be a difference between what can be inferred from the model and what is the case in reality. I appreciate your response.