FreeLists / si-list / [SI-LIST] Re: HSPCIE Simulation about Transmission Line

["Tracy Barclay" <Tracy.Barclay@xxxxxxxxxxxx>]

 James and Zhangkun,

In HSPICE, extremely short transmission lines can cause poor performance.
This is due to the time step control algorithm when the W Element is static.
Since the breakpoints are set after each minimum delay time, you will end up
with too many redundant time points being calculated when the signals at the
terminals of the transmission line do not vary rapidly.

In the newest version, W-2005.03, a dynamic time step control algorithm was
added.  The necessary time points are set dynamically according to the
variations of terminal currents and voltages.  To enable the W element
dynamic timestep control algorithm, the option WACC should be set.  The
syntax is:

.option WACC=<value>

The default for the WACC option is 0 and the original fixed timestep
algorithm will be used.  The option can be set between to positive, real
values between 0 and 10.0.  When WACC greater than 0, the dynamic timestep
method is activated.  Larger values result in higher performance with lower
accuracy, while smaller values result in lower performance with better
accuracy.  For most simulations, a value of WACC=1.0 is suggested.  For more
accurate simulations, a value of WACC=0.1 is suggested.

Tracy Barclay
CAE
Synopsys
 
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of James Church
Sent: Thursday, April 07, 2005 11:47
To: zhang_kun@xxxxxxxxxx
Cc: si-list
Subject: [SI-LIST] Re: HSPCIE Simulation about Transmission Line

Hi Zhangkun,

This is a fairly well known problem with certain versions/vendor's spice 
algorithms. Extremely short transmission lines often have a very hard 
time converging and will occasionally have large errors or not converge 
at all.

I would recommend using a distributed rlc network for these short lines.

James

Zhangkun wrote:

>Dear all
>In the current simulation, I meet one problem. When there is short
transmission line in the netlist, the simulation is very slow.
>
>For example, in my netlist, there is the following sentence
>
>wline_trunk01 node1      vss rseries1  vss rlgcfile=sline_50.rlgc n=1
l=1800mil
>wline_trunk02 rseries2   vss stub_01   vss rlgcfile=sline_50.rlgc n=1
l=6500mil
>wline_trunk03 stub_01    vss stub_02   vss rlgcfile=sline_50.rlgc n=1
l=200mil
>wline_pull    stub_02    vss pull      vss rlgcfile=sline_50.rlgc n=1
l=200mil
>
>wline_stub01 nd_out_01a vss nd_out_01 vss rlgcfile=sline_50.rlgc n=1
l=200mil
>wline_stub02 nd_out_02a vss nd_out_02 vss rlgcfile=sline_50.rlgc n=1
l=200mil
>
>If the length of the wline_stub02 is set as 10mil, the simulation would
become very slow. Could anybody tell me the reason.
>
>Best Regards
>
>Zhangkun
>2005.4.7
>
>
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