Electronics Forum / CAD / October 2005

Eh?  How can that be?  Simulation speed is circuit-content dependent.

                                       ...Jim Thompson

           
I love to cook with wine.      Sometimes I even put it in the food.

Thank you for your reply.

SPICE3 is the spice program for unix.
WHat does 'ecipsTL' mean?

Hello Brett,

The first message from Vivian contained no information about
the simulated circuit. How could somebody give any useful
advice except running it on the fastest PC?

After the second posting from Vivian we have got informed that
it is a ring oscillator. I expect now that it's an odd number
of inverters in a loop. There is still no detailed information
about the circuit, e.g. the number of stages. It makes a big
difference whether you use 3 or 31 inverters.
In the ladder case the simulation time will be 10 times longer.

After the third message we know it's any SPICE-3 simulator
under Unix. Something self compiled?
Who can give any advice for an unknown program?

---
Hello Vivian,

I have tried now with an 11 stage ring oscillator which oscillates
at about 1.8GHz. The extrapolated simulation speed on the fastest
edge P4 or AMD64 would be about 20ns per second of simulation time
with the high precision setting for the LTspice-simulator(default).
This speed can be increased by factors(2 to 5) when the accuarcy
requirement will be decreased. The important parameters in LTspice
are reltol and trtol.

It's still not specified how many micro seconds.
Let's assume he wants 40us.
This would require in my case 2000seconds when using the
high precision simulator settings. The amount of data may be
in the range of 20 millions data points per saved node voltage.

* Please remember that these are results for my circuit
* which is most probably not the circuit from Vivian.
* Maybe he has used less inverter stages which gives
* a shorter simulation time.

Conclusion:
Ring oscillators cause a lot of transitions where SPICE
automatically has to decrease the timestep to get useful results.
The number of circuit nodes also increases with more stages.
Overall the simulation time has been roughly proportional
to the number of inverter stages.

Best regards,
Helmut

LTspice is an unlimited free SPICE program with GUI from Linear Technology.
http://ltspice.linear.com/software/swcadiii.exe

There is an independent user group.
http://groups.yahoo.com/group/LTspice/

[snip]

I may be "self-absorbed", but I'm not clueless, as you appear to be.

                                       ...Jim Thompson

           
I love to cook with wine.      Sometimes I even put it in the food.

Brett, you just elected yourself to the a.shole status IMNSHO.  Some of
these people are very helpful SPICE experts.  They can also get distracted
talking to past and around each other and not answer OP.  If you really
want them to help, post your netlist or if it is large put it on a web page
or some other publicly accessable place.  And help you will normally get.