[SI-LIST] Re: Hspice differential Tline

  • From: "Brown, Mike (Austin, TX)" <mibrown@xxxxxx>
  • To: <timoceous@xxxxxxxxx>, <swldstn@xxxxxxxxxxxx>,"si" <si-list@xxxxxxxxxxxxx>
  • Date: Wed, 15 Oct 2003 14:42:36 -0500

One might suspect that the difference is the fact that the CM reflection =
coefficient is 1 for the parallel termination and near 0 (slightly =
negative) for the split 50 ohm terminations.

Is the ringing in-phase at the + and - nodes of the termination?

Mike

-----Original Message-----
From: timoceous [mailto:timoceous@xxxxxxxxx]
Sent: Wednesday, October 15, 2003 12:45 PM
To: swldstn@xxxxxxxxxxxx; si
Subject: [SI-LIST] Re: Hspice differential Tline


Hi Guru,

   First of all, I would like to thank all those
who have replied.  Secondly, maybe I should explain
more on what I am seeing; I am simulating two sets of
terminations on the LVDS:

1) parallel termination.
(100 Ohm in between outputs at the far-end of Tline).

2) Shunt termination with vterm=3D1.2v
(50 Ohm to vterm at the far-end of Tline).

3) All using ideal T line.

   What I am noticing is that the shunt termination
does not "ring" regardless of the delay of the T line.
 But with the parallel termination the ringing would
happen depends on the delay of the line.  I am not
sure why, can someone shine some light into this?

   Obviously, I am looking at the signal positive and
negative separately.  One can question that I should
have looking at signal differentially.  But, there
will still be difference with different delays(in this
case rise and fall time variation).  On the other hand
with shunt termination, it seems perfect.

Thanks in advance,

Tim
  =20
--- "Steven M. Waldstein" <swldstn@xxxxxxxxxxxx>
wrote:
> Tim,
>=20
> I'm not sure how to do specifically what you want
> but I can tell you its very easy to use Welements
> instead of Tlines and enter your actual board
> stackup
> to the field solver and get either differential
> striplines
> or microstrips in Hspice.
>=20
> Thats what we use. We have a whole series of
> 1,2,3,5,10
> line microstrip and stripline templates. We use
> these for
> xtalk simulations as well.
>=20
> If you want more info on this let me know. I'll pass
> it on.
>=20
> Steve Waldstein
> swldstn@xxxxxxxxxxxx
>=20
>=20
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of
> timoceous
> Sent: Tuesday, October 14, 2003 8:32 PM
> To: si
> Subject: [SI-LIST] Hspice differential Tline
>=20
>=20
> Hi Guru,
>=20
>    I would like to know if there is a way to=20
> connect the hspice "T" element (ideal) to model
> differential transmission line.  For instance, model
> a pair of LVDS Tline.  I have tried but got lots
> of reflection/ringing at the output.  Here is what
> I have tried:
>=20
> T1 Doutp GND VOP GND Z0=3D100.0 TD=3D500E-12 +IC=3D0.0 0.0
> 0.0 0.0=20
> T2 Doutn GND VON GND Z0=3D100.0 TD=3D500E-12 +IC=3D0.0 0.0
> 0.0 0.0
>=20
> Rpa VOP VON 100
>=20
> Note: Doutp/n are the LVDS driver output.
>=20
> Thanks in advance,
>=20
> Tim
>=20
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