[SI-LIST] Re: spice math question

Hi Andy,

Iw as using primarily modal models which are a combination of tlines and
dependendent voltage and current sources.

However...

I just did some experiments with pure 50 Ohm t-lines.

For 40 inches at td=158p/in.  td should equal 6.32ns.

When I simulate a single 40 inch tline I get 5.89 ns 50% to 50% delay with a
100ps edge(0 to 100%) input.

10 sections of 4 inches each  yields td=6.16ns
20 sections of 2 inches each yields td=6.3 ns.

I'd appreciate a reality check on this.  I terminated the far end of the
tline in 50 Ohms to ground.

John


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Ingraham, Andrew
Sent: Wednesday, October 30, 2002 10:42 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: spice math question


Which kind of transmission line model?

If you are using the basic T-element lossless transmission lines, I
think SPICE *ought* to be accurate.  I am not aware of a rounding error.

SPICE effectively implements T-element transmission lines using two raw
delays (one for each direction), a couple of controlled sources, and
resistors.

On the other hand, (1) I have been told that Hspice had problems with
T-element transmission lines at one time, and (2) if you measure
pin-to-pin, or by measuring the insertion delay due to adding a t-line,
you might not get the exact delay you ask for, depending on the
terminations on both ends.  This happens in reality too.

Cascading shorter T-element t-lines *should* produce the same result.
Interesting that it doesn't.

Andy



------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List archives are viewable at:
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages 
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: