RE: [SI-LIST] : Urgent help needed on HSPICE simulation

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From: Lynne Green (lgreen@mail.hyperlynx.com)
Date: Tue Aug 01 2000 - 13:13:03 PDT


How to outsmart SPICE:

Use .NODESET to SUGGEST a starting point for convergence.
SPICE will converge starting from this voltage. Useful when
there are multiple DC operating points possible, or when there
is a lot of feedback in the circuit (e.g. transistor junction
capacitances).

Use .IC (together with the TRAN Use IC command) to FORCE
the voltage at convergence. Useful when you want to start
a transient run from a non-stable point. If you do this and let
the simulation run to a long STOP time, with no changes on
the input sources, you can find what DC point SPICE thinks it
wants to converge at.

There are MANY reasons for not converging, from a latch that
has no preferred DC state, to a very large circuit with feedback,
and many many more. SPICE books usually have an entire chapter
on this.

Large voltage swings at receiver could indicate an unterminated
transmission line. Many other possibilities.

Also, check node naming on the circuit, especially if you are
using differential drivers or receivers. If you print out a node
list in SPICE, you might see some unintended "shorting".

Lynne

Dr. Lynne Green
Product Marketing Engineer
HyperLynx, A Division of PADS Software, Inc.
14715 NE 95th St, Suite 200
Redmond, WA 98052
425-497-5081
FAX 425-881-1008
lgreen@hyperlynx.com
http://www/hyperlynx.com

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Perry Qu
Sent: Tuesday, August 01, 2000 11:40 AM
To: si-list@silab.eng.sun.com
Subject: Re: [SI-LIST] : Urgent help needed on HSPICE simulation

Hi!

Refering to my question 2 posted this morning, I found that the simulation
results are
quite different depending on how you specify and whether you specify the DC
operating
point for the device. Is there any general guideline on we should specify
the DC point
using .ic or .nodeset, etc. in HSPICE ? What could be wrong if I got the
following error
message:

"**error**: no convergence in operating point"

Thanks in advance.

Best Regards

Perry

Perry Qu wrote:

> Good morning, everyone:
>
> Thank you for your help on my previous question posted on the SI list. I
tried out
> the SPICE simulation that you guys suggested and I have the following
problems:
>
> 2. In another case, I used a driver with SPICE model to drive a LVDS
differential
> receiver with IBIS model. The voltage swing I got at the receiver pin much
larger
> than the LVDS specifications. Do you have any idea what could be wrong ?
>
> Thank you very much for your help.
>
> Best Regards
>
> Perry
>
> SI Specialist
> Alcatel CID
> Kanata, ON, Canada
> Tel: (613) 7846720

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