[SI-LIST] Re: 50 ohms cable model
- From: steve weir <weirsi@xxxxxxxxxx>
- To: gerald.truong@xxxxxxx, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 23 Nov 2005 10:42:01 -0800
Gerald,
Your individual LC networks probably have a time constant that is much too
long. The "bucket brigade" approximation only works well when the time
constant of an individual cell is 10% or less the signal rise-time. Eric
Bogatin's "Signal Integrity Simplified" deals with the "bucket brigade"
approximation rather nicely. But given that this is a cable, why don't you
use a Tx line model?
Steve.
At 10:26 AM 11/23/2005 -0800, Truong, Gerald \(Space Technology\) wrote:
>Hello SIGurus,
>I modeled a 50 ohms cable using the data in cable's datasheet. The
>equivalent distributed L and C yield 50 ohms but when I run the
>simulation with a buffer that has a 50 ohms source impedance, the
>results exhibit overshoot. When I run the simulation with the buffer
>connected to a 50 ohms trace, the results yield a waveform with no
>overshoot, as I would expect in a perfectly match transmission line
>environment.
>
>Does anyone have an explanation for why the 50 ohms cable induces
>overshoot?
>
>Thank you for your time.
>
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