Re: [SI-LIST] : Parallel single-ended traces routed to achieve 35Ohm controlledimpedance

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From: Vinu Arumugham (vinu@cisco.com)
Date: Tue Oct 31 2000 - 13:44:11 PST


"Ingraham, Andrew" wrote:

> Sal, I don't know if what you suggested has been tried before, but I think
> it ought to work. To the extent that the two layers are isolated from one
> another, you ought to get exactly half the impedance of each line alone.
> Vias at intervals (much closer than a wavelength apart at your highest
> harmonic frequency) might be good; but the higher in frequency you go, the
> more vias are called for, yet the more they look like discontinuities.

Vias between the lines are not needed at all for this application. Imagine
the routing as simply being a ring topology with the driver and receiver
being at diametrically opposite ends of the ring. If the ring is constructed
using a 70 ohm transmission line, the driver sees a 35 ohm line.

Thanks,
Vinu

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