RE: [SI-LIST] : Clock tree

George Harris ([email protected])
Thu, 6 Aug 1998 14:45:10 -0400


What I usually do when several consumers are grouped close together is
run etch from the clock source to a point about midway between loads and
"fairly close" to them, and then run short pieces of etch to each
individual load. All these short pieces must be of equal length L, and
the common piece should be several times greater than L, and L should be
not over 1.5" because there will be some reflections from the loads.(I
assume you are working with fast edges and relatively high clock

I assume that you are going to use Spice to try various configurations.
Depending on the clock driver you may want to use 2 or 3 sections of the
driver in parallel, possibly with 10 ohm resistors in series with each
placed near the driver. It may also be useful to use wider etch (lower
Zo) in the common lead, to better match to the Zo/n which the junction
will see.

50 ohm
USE ZO=25 OHM /--------rcvr1
driver -----------------------o 50 ohm n=2

> ----------
> From: [email protected][SMTP:[email protected]]
> Sent: Thursday, August 06, 1998 1:57 PM
> To: [email protected]
> Subject: [SI-LIST] : Clock tree
> is any one build clock tree on large board.
> what is the best way to build the clock tree ?
> I connect the same clock to few consumers which are very close ? is
> that
> O.K ? what is consider as "close" ?
> what is the best termination and connection for that ?
> Best regards
> Shimon Turgeman