RE: [SI-LIST] : transmission line theory

Greg Edlund (Greg.Edlund@digital.com)
Tue, 3 Mar 1998 13:05:37 -0500

Andrew,

Here's some stuff from my little library. I heard the last paper at
DesignCon98 and thought it was really good.

"MECL System Design Handbook," Blood, Motorola #HB205.

"Transmission Line Effects in PCB Applications," Motorola Application
Note AN1051. (To order, check out their web page.)

"High-Speed Digital Design," Johnson and Graham, PTR Prentice Hall,
1993.

"Network Topology Analysis Using the Reflection Coefficient," John
Grebenkemper (Tandem), presented at DesignCon98. (For proceedings, see
www.designcon.com and pull down the "List of Contents" menu.)

----------
Greg Edlund, Principal Engineer
Server Product Development
Digital Equipment Corp.
129 Parker St. PKO3-1/20C
Maynard, MA 01754
(978) 493-4157 voice
(978) 493-0941 FAX
greg.edlund@digital.com

----------
From: Bodley, Andrew[SMTP:andrew.bodley@intel.com]
Sent: Tuesday, March 03, 1998 11:50 AM
To: 'si-list@silab.eng.sun.com'
Subject: [SI-LIST] : transmission line theory

Hi All,

I am interested in transmission line theory as suggested
by Mark
below. Does anyone have suggested references both basic and
intermediate?

Thanks
Andrew Bodley
andrew.bodley@intel.com

> I find it necessary to go back to transmission
>line theory (reflection coefficients, etc.) and make
sure what
I'm
>simulating makes sense!

> -----Original Message-----
> From: Greg Edlund [SMTP:Greg.Edlund@digital.com]
> Sent: Tuesday, March 03, 1998 5:06 AM
> To: 'Mark Nass'
> Cc: 'si-list@silab.eng.sun.com'
> Subject: RE: [SI-LIST] : Driver Strength
>
> Mark,
>
> I have found that driver current ratings don't mean a whole
lot today.
> They are a hold-over from TTL days, when each receiver drew a
certain
> dc
> current and a driver had to be able to source the dc current
of all
> its
> loads. In a CMOS environment, they are useful in a relative
sense,
> i.e.
> you can guess that a 4 mA driver will probably have a lower
output
> impedance than a 2 mA driver - within the same part family and
the
> same
> vendor. However, don't expect vendor A's 4 mA driver to have
the same
> output impedance as vendor B's 4 mA driver.
>
> Output impedance tends to be a much more useful parameter in a
> transmission line environment. Unfortunately, most vendors
don't spec
> output impedance. If you have a non-linear output IV curve,
it does
> vary over loading, making it a little difficult to spec. The
vendor
> would have to guess what kind of environment driver will see
and spec,
> say, a 60 Ohm resistive load to ground and Vdd. Even this
information
> is more useful than nothing.
>
> The best thing you can do is to ask for an IBIS model of your
driver
> that is verified against lab data.
>
> How many loads you can expect to drive varies widely with load
> capacitance, net topology, and timing. A behavioral simulator
is an
> excellent tool for prototyping nets and answering these kinds
of
> questions. It's important not to rely on the simulator to do
all your
> work for you, though. I find it necessary to go back to
transmission
> line theory (reflection coefficients, etc.) and make sure what
I'm
> simulating makes sense!
>
> ----------
> Greg Edlund, Principal Engineer
> Server Product Development
> Digital Equipment Corp.
> 129 Parker St. PKO3-1/20C
> Maynard, MA 01754
> (978) 493-4157 voice
> (978) 493-0941 FAX
> greg.edlund@digital.com
>
> ----------
> From: Mark Nass[SMTP:markn@rccorp.com]
> Sent: Monday, March 02, 1998 10:35 PM
> To: si-list@silab.Eng.Sun.COM
> Subject: [SI-LIST] : Driver Strength
>
> Can someone explain to me what driver strength means?
When
> a driver is spec'd by an ASIC vendor as a 12ma, 6ma, etc
what
> does
> that mean as far as its expected VI curve and how many
loads
> I can expect it to drive?
>
> Thanks,
> Mark Nass