Target

The target impedance is set in the Target line. Two parameters are used. Target impedance (enter value in mili-ohm) and frequency (enter value in Mega Hertz).

See the target line in the graph as the blue curve. When using the optimizer, it will try to push the impedance curve under the target line.

pdntool_target

Impedance

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Frequency

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2 thoughts on “Target

  1. I’m curious why you roll off the target impedance as you approach 100MHz? I believe Lee Ritchey advocates for simply “keep Z below the target up to 150MHz” and several other sources I’m familiar with suggest the same to 100MHz.
    The exact f_max I’m not concerned with, to me that’s a design choice, but I’m interested to know why you added a roll off.
    Thanks

    • You set the frequency, so that is up to you. The roll-off itself is pretty steep (so almost a sharp corner) and not directly rooted in any specific theory. It is clear that the “correct” (whatever that means in this situation) requirement cannot be a sharp corner. If you look at energy over frequency for digital signals there will be some roll-off. If you look at the L’s and C’s of going from board to die in through the package etc., that will also form a filter with a roll-off. What this all adds up to is often not simple to describe. A steep roll-off as used here is likely every bit as good as a sharp corner requirement for all practical purposes. Hope this helps.

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