# RE: [SI-LIST] : eye diagram in HSpice

From: Greim, Michael ([email protected])
Date: Wed Dec 20 2000 - 08:32:49 PST

Hi Vittorio,

This has been discussed many times before on this
list, and yet it still remains a confusing issue.
I will try to keep what should be a simple topic
simple. First cut and past the following into your
favorite spice deck desiring an eye display

**************** cut here **********************

*****************************************************************
* Setting up the eye diagram display
* To display the eye pattern for the simulation, click on t
* under voltages in awaves and assign it to the x axis.
* Note that display period is twice the period of the freq
* specified below.

.param eyefreq=625e6 per='1/eyefreq' \$ max toggle lvds rate
.param Tshift=1.55n
eT T 0 VOL='((TIME-Tshift)*(eyefreq/2))-int((TIME-Tshift)*(eyefreq/2))'
rT T 0 1k
.print tran v(t)

*****************************************************************

***************** cut here too *******************

What the above does is creates a variable that is used to
replace the x axis of your display. This variable essentially
goes from 0 to a time equalling your period and then resets to
zero. This allows the display to be re-written over and over
creating the eye. The eyefreq variable is your data rate or
twice your toggle rate. The above illustrates an eye for a
625 MBS signal, or 312.5 Mhz signal. The tshift variable allows
the eye to be centered in your display. A non-centered eye can
offer some pretty interesting displays.

If you are in avanwaves click on t or v(t) in the curves window
Now go down to the current x-axis window and click apply. You
have now replaced linear time on the x axis with your new variable.

double click on a signal that you wish to see and voila,
an eye pattern. If you are looking at a clock, this will
be pretty uninteresting. However, if you are looking at
the output of a psuedo random pattern driven network you
should have something that looks like what you see in all
the high speed articles.

I hope that this allows you to get up and running. In the
beginning I always knew the block of spice to add to my deck,
just not what to do with it after the simulation was complete.

best regards and happy holidays,

Michael Greim

'Making the world safe for digital signals anywhere'

-----Original Message-----
From: Ricchiuti Vittorio [mailto:[email protected]]
Sent: Wednesday, December 20, 2000 10:45 AM
To: [email protected]
Subject: [SI-LIST] : eye diagram in HSpice

Hi all.
I have some problems to display the eye diagram of a pseudorandom pattern in
HSpice simulations. The technique that Avant! appliction note suggests is
not so good in my opinion.
statements to display eye diagram ?

Regards
Vittorio

ing. Vittorio Ricchiuti
Siemens ICN
Loc. Boschetto
67100-L'Aquila
ITALY
Tel: +39/0862/335880
Fax: +39/0862/335623
e-mail: [email protected]

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