[SI-LIST] Re: Lumped capacitance estimation
- From: "Andrew Ingraham" <a.ingraham@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 6 Apr 2005 12:04:48 -0400
> 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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