Re: Differential clock

Howard Johnson (howiej@sigcon.com)
Mon, 14 Apr 97 16:07:13 PDT

I have found differential distribution of clocks to
be a very effective means of combating
gound bounce in the transmitting package,
ground bounce in the receiving package,
as well as the ground shifts that occur
on either side of the connectors in high-speed
multi-drop bus systems.

I have found differential distribution of clocks
to be of little value in reducing the impact of
crosstalk generated locally by other traces on
the same PCB. This is becuase the crosstalk
function from nearby traces falls off very steeply
with distance, so one clock trace is inevitably
affected more than the other. I find that I
still have to separate the clock from other signals
to limit crosstalk.

Best Regards
Dr. Howard Johnson

>Errors-To: si-admin@silab.Eng.Sun.COM
>Date: Wed, 9 Apr 97 9:25:52 EDT
>To: <si-list@silab.Eng.Sun.COM>
>From: "fabrizio zanella" <fabrizio=zanella%Eng%EMCHOP1@fishbowl02.lss.emc.com>
>Subject: Differential clock
>
>Hello SI engineers,
>I understand the benefits of using differential pairs for signals running
>at 100MHz and above. Can anyone speak about the impact of using
>differential clocks in a parallel bus, though? Do the differential clocks
>maintain the noise suppression characteristics when daisy chained in a
>multidrop environment?
>Has anyone tried this and had positive experiences vs. single ended
>multidrop clocks?
>
>Thanks in advance,
>
>Fabrizio Zanella
> _/ _/ email:
>zanella_fabrizio@emc.com
> _/_/_/_/ _/ _/ _/_/_/ _/ voice: (508) 435-1000 Ext.
>4645
> _/ _/_/ _/_/ _/ _/ Fax: (508) 435-8949
> _/_/_/_/ _/ _/ _/ _/ _/_/_/
> _/ _/ _/ _/ EMC Corporation
> _/_/_/_/ _/ _/ _/_/_/ 171 South Street
> Hopkinton, MA 01748-9103
>
>
_________________________________________________
Dr. Howard Johnson, Signal Consulting, Inc.
16541 Redmond Way, Suite 264, Redmond, WA 98052
U.S. tel (206) 556 0800 // fax 206 881 6149 // email howiej@sigcon.com
http://www.sigcon.com