Subject: RE: [IBIS-Users] time shifted edges
From: Angulo, John (john_angulo@mentorg.com)
Date: Mon Aug 18 2003 - 16:10:05 PDT
Erik,
The model's V-T tables dictate to the simulator when to start the buffer's edges. When you see a time shift in the simulated edges relative to your V-T tables, it probably means that the tool is clipping some of the lead-in time from the tables before simulation. This is useful for those models that contain excessive lengths of dead time before the launch of the waveforms (we've seen ten nanoseconds in some cases), but it is undesirable in LVDS or other applications with carefully constructed V-T tables for precise duty cycle timing. Hyperlynx lets you turn lead-in clipping off. I'll contact you offline to point out the exact option.
Best regards,
John Angulo
Hyperlynx Products
Mentor Graphics Corp.
john_angulo@mentor.com
425-869-2320
-----Original Message-----
From: erik.van.der.ven@philips.com [mailto:erik.van.der.ven@philips.com]
Sent: Monday, August 18, 2003 12:56 AM
To: ibis-users@eda.org
Subject: [IBIS-Users] time shifted edges
Dear IBIS colleagues,
I am trying to model a differential LVDS output buffer.
I have generated waveform tables from Spectre simulations. The falling and rising waveforms look fine at first glance.
In Spectre the falling and rising waveforms (of both outputs, which are equal) have a crossing point about in the middle of the DC level (high and low state).
When I simulate my model with Hyperlynx I see that the crossing point is at a very low level, because of a time shift of the edges. I simulate with an Rfix (50 Ohm) to a Vfix which is
in the middle of the DC levels.
So my question is:
How does a simulator determine where the edges start? Do different simulators use the same algorithm for this?
What can I do to get crossing point in the right place? (or: how do I control the place (in time) of the edges?).
Can anyone help me? Thanks in advance.
With kind regards,
Ir. Erik van der Ven
Room DB1032
Business Line Networking Infrastructure
Philips Semiconductors BV
Gerstweg 2
6534 AE Nijmegen
The Netherlands
Phone: +31-24-3534334
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