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DS30EA101: Input Termination Resistor and AC Caps

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Part Number: DS30EA101

The datasheet recommends the following configuration at the input to the DS30EA101:

    

If instead at the input the ac caps and the terminating resistor locations are reversed as shown below, what would the implication be? Would the DS30EA101 operate as behaved? Why does the ac cap need to be located closest to the input of the device instead of the terminating resistor? Is there a difference electrically?

Thanks,

Mark Heh

  • Hi Mark,

    I was unable to view the images you attached, but I think I am able to get the gist of what you are requesting.

    In the figure, we typically place the AC coupling capacitors after the terminating resistor so that the impedance discontinuity of the AC coupling cap does not contribute to the effect of any reflections at the 100-ohm terminating resistor. Typically, we recommend for all high-speed applications that the AC coupling cap be placed closest to the device input so as to minimize the effect of reflections due to the increase of the capacitor pads in comparison to the trace width. This is the preferred method for layout.

    With that having been said, I believe you can still function without issue when the terminating resistor is before the AC coupling cap. Is there an issue causing you to require placing the cap before the terminating resistor?

    Thanks,

    Michael

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