[SI-LIST] Re: Convergence problem after inserting detailed connectormodel
- From: "Hassan O. Ali" <hassan@xxxxxxxx>
- To: julia.nekrylova@xxxxxxxxx
- Date: Fri, 20 Feb 2004 00:37:08 -0500
Julia,
I've come across this problem so many times. I think it is caused by
components in the connector model that have too small values. Small
elements combined with big elements in the rest of your netlist result
in an ill-conditioned matrix equation. An ill-conditioned matrix
equation behaves differently with different solution methods. That
explains why changing the solution method to Gear solves the problem
sometimes.
Here are a few things that I normally do when I face problems with
connector models:
1. I make sure I terminate all un-used connector terminals with 50-ohm
loads - on both sides (input and output)
2. I replace all insignificant resistor values (e.g. below 1e-4) with
zero DC voltage sources
3. I connect 1G shunt loads to all the terminals
4. I add appropriate via parasitics (especially capacitance) to all the
connector terminals
5. I run the simulation in stages and observe convergence issues:
i) just the connector with ideal source and load on one pin
ii) full netlist with no transmission lines between connector and
the rest of the network (i.e. direct connection)
ii) full netlist with lossless transmission lines (the T elements)
between the connector and the rest of the network
iii) full netlist with W-element transmission line models between
the connector and the rest of the network
6. If only the connector model with ideal source and load runs, I
generate a connector macro-model through frequency-domain S-parameters
obtained using AC analysis.
Hope that helps.
Hassan.
Nekrylova, Julia wrote:
>Hello,
>
>
>I've added a detailed connector model to my Hspice deck and started
>getting
>
>"internal timestep too small" error messages. Before that the connector
>was represented just by
>
>RLGC matrix model. Tried different fixes: reduced transition times, set
>initial conditions,
>
>tried gear method, put shunt conductances and capacitances. Some times
>in the past Accurate=1 and
>
>Converge=4 worked for me, but this time nothing seems to help.
>
>
>
>What else I could try? I am pretty sure there are lots of people on the
>list who had similar problems
>
>with their spice decks after adding sophisticated interconnect models.
>
>What could be the most popular solution in this case besides talking to
>the connector company application engineer?
>
>
>
>Thanks a lot,
>
>Julia
>
>
>
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