Re: SPICEing The Inductance of a Trace Over a Ground Plane?

D from BC wrote:

On Mon, 17 Sep 2007 20:38:29 -0700, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:


On Tue, 18 Sep 2007 02:27:00 GMT, D from BC <myrealaddress@xxxxxxxxx>
wrote:


[snip]

Aside from the 50% signal loss, invalid CMOS levels and a hot pulse
generator...the great is the 10cm strip acts like it's not even
there....if I got that right..


D from BC



You can also "source terminate" a transmission line....



<-------tx line-------------->

+5v +5v
| |
| |
gate----R1------------------------------gate
driver receiver
| |
| |
gnd gnd



If R1 is close to the driver and equal to the line impedance, you get
a perfect 5 volt step at the receiver, no problems, no ringing, no
static power dissipation.

John



I think I read somewhere that open ended transmission lines can
reflect..


They always do. However, when it's source terminated as John wrote the reflected energy dissipates at the source terminator.

I am not a big fan of source terminators since they waste energy. They also halve the arriving fast pulse amplitudes which may or may not cause problems. AC terminators are nice. You place a terminator at the end with a capacitor in series that is just a tad larger than needed to deal with the frequencies above where the length of line would causes any issues, but not much below.


I haven't given it much thought yet and don't know if it's a digital
concern.

I'm wondering if PC motherboards use some sort of termination for long
PCB traces passing high speed digital..?


The good ones? Oh yes.

--
Regards, Joerg

http://www.analogconsultants.com
.

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