FreeLists / si-list / [SI-LIST] Re: Lumped capacitance estimation

["Andrew Ingraham" <a.ingraham@xxxxxxxx>]

>          I need to calculate equivalent lumped capacitance seen by an IO
> driver which  is connected to PCB trace (approx 3 Inches) and then cable.
> The average rise/fall time is 600ps. I have information about the PCB
> trace capacitance/inches. Will my assumption  be correct if I take
> PCB-trace length (for lumped-capacitance calculation) which provides 300ps
> delay.

For lumped capacitance, just multiply capacitance/length times the length.

The rise/fall time doesn't make any difference as far as equivalent lumped
capacitance is concerned.  However, if the rise/fall time is fast enough,
you shouldn't be using a lumped capacitance in simulations.

Are you sure your PCB trace delay is only 100ps/inch?

> What would be the best way to simulate IO driver as far as rise/fall time
> accuracy is concerned assuming lumped model for Tx line.

For accuracy, best way = abandon the lumped model for the line.

What did you mean by "best way" anyway?  If you have an I/O driver model and
a transmission line model, just simulate them and look at the results.

Regards,
Andy


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