Re: [SI-LIST] : RE: [SI-LIST]: Long bus or star?

Vinu Arumugham (vinu@cisco.com)
Tue, 30 Mar 1999 11:25:14 -0800

Consider 5 matched spokes of 50 ohm each. If the driver at the hub has an output impedance of 10 ohm, there would no need for any series source terminators for impedance matching. However, if the driver cannot supply the large
switching current without affecting its reliability, one would need to introduce series resistors at the hub (thus introducing an impedance mismatch). This will cause the step going down the spokes to be less than half height and
the loads may fail to switch on the incident wave, requiring multiple reflections to reach the final voltage level.

Vinu

Jon Keeble wrote:

> Seems to me that a classic series source terminator of value Zo at the hub,
> one for each spoke, is optimum. It halves the required drive, and turns the
> voltage doubling at the open circuit at the end of each spoke to advantage.
> The reflections witl be fully absorbed back at the hub in the resistors.
>
>

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