RE: [SI-LIST] : Ground gap problem

Bob Davis (bob@scsi.com)
Wed, 24 Mar 1999 21:29:23 -0800

Gents

The figures are in the Q2/88 version of the HB205 MECL System Design
Handbook... Be careful and look at the way that the planes are cut to see
the results. The gap in the plane was for example is 2.5 INCHES. The
reflection on pg137 shows the distance of the changed impedance to be for 5
inches (2.5 inches X2) at ~154ps/inch for a surface trace.

The examples on pg140 tend to indicate that these are .062 board thickness
1oz copper and 100mil width for 50 ohms (checks with the UltraCAD
Calculator). This may not be indicative of crossing .005 to .010 gaps in
split planes with 4 mil lines at 6 mil height.

Bob Davis, Consulting Engineer
Summit Computer Systems, Inc.
Signal Integrity Specialists
Bob@scsi.com, www.scsi.com
(408)353-2706
(408)353-8116 FAX

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com] On Behalf Of Howard Ji
Sent: Wednesday, March 24, 1999 7:43 AM
To: si-list@silab.eng.sun.com; si-list@silab.eng.sun.com
Subject: Re: [SI-LIST] : Ground gap problem

John,

What version of the Motorola handbook you have? I have a 96 version and I
couldn't finder those finures.

At 05:26 PM 3/23/99 -0800, John Lockwood wrote:
>
> Sangil,
>
> Motorola's MECL System Design Handbook has a few TDR plots which show the
> effects of cutting ground under traces. See figures 7-11 on page 137 and
7-13
> on page 139.
>
> At 02:09 PM 3/23/99 -0800, you wrote:
> >>>>
>>
>> Hi all,
>> I am trying to find the effects of the gaps on the ground plane for the
>> high-speed circuits.
>> Even though I have a couple of references about the via, which has the
>> ground gap problem, I need more specific data about the ground gap
problem
>> regarding the gap size, gap location.....
>> Either measured data or simulated data will be fine ( papaers or refernce
>> book...)
>> Looking forward to your answers.
>>
>> Thanks
>> Sangil Lee
>>
>>
>>
>
> <<<<
>
>
>
> John Lockwood
> Juniper Networks
> johnl@juniper.net
> Phone 650-318-3305
>
>
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