FreeLists / si-list / [SI-LIST] Re: AC coupling matching

[Vinu Arumugham <vinu@xxxxxxxxx>]

"N. Paul Taddonio" wrote:

> Dear SI-List
>
> Can anybody comment on the effect of AC-coupling capacitors used
> on a pair of matched length (200 MHZ HSTL) clocks?  I have duplicated
> the capacitor placement (near the driver), ie the trace lengths are all
> matched, but the capacitors themselves are not matched parts.
> Any guesses as to how much skew could be induced?
>

~1 ps ? The difference in series impedance between a 470 pF and a 390 pF
capacitor (~20% mismatch) @ 400 MHz appears to be < 0.1 ohm.

>
> The capacitors are 470 pF 10% X7R 0603 type. The value was chosen
> for minimal impedance around 200 and 400 MHz.
>
> -Paul
>
> --------------------------------------------
> N. Paul Taddonio
>
> Nortel Networks, Optical Ethernet Switching
> 600 Tech Park, Billerica, MA 01821, (mailstop E65-60-203)
> phone: 978-288-4611               fax: 978-288-0620
> email: ptaddoni@xxxxxxxxxxxxxxxxxx
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