Speeding up temperature dc-sweep.

[Svenn Are Bjerkem]

Hi,
When a circuit take long time to find its dc-point, it is recomended to
use the write=spectre.dc and then readns=spectre.dc as a "seed" to find
the dc-point. This also normally speed up the finding of the operation
point.

Now I am doing a dc-simulation with a temperature sweep. I cannot see
any difference in simulation speed if I use the readns=spectre.dc or
not. From the timestamp of the spectre.dc file, I see that it is
written once at the start of the simulation, then no more. This lead me
to suspect that it is also only read once during startup, and then no
more, hence it is not possible to speed up a dc-sweep this way. I know
that the circuit has some problems with convergence, and thus really
expected a speed up.

Any idea?
--
Svenn

 

[Andrew Beckett]

On 30 Oct 2006 06:46:44 -0800, "Svenn Are Bjerkem" <svenn.are@bjerkem.de> wrote:

Hi,
When a circuit take long time to find its dc-point, it is recomended to
use the write=spectre.dc and then readns=spectre.dc as a "seed" to find
the dc-point. This also normally speed up the finding of the operation
point.

Now I am doing a dc-simulation with a temperature sweep. I cannot see
any difference in simulation speed if I use the readns=spectre.dc or
not. From the timestamp of the spectre.dc file, I see that it is
written once at the start of the simulation, then no more. This lead me
to suspect that it is also only read once during startup, and then no
more, hence it is not possible to speed up a dc-sweep this way. I know
that the circuit has some problems with convergence, and thus really
expected a speed up.

Any idea?

Hi Svenn,

If you're doing the sweep of temperature as the dc sweep, then each point
will start from the previous solution point anyway. readns will only help with
the first.

From spectre -h dc:

16 write File to which solution at first step in sweep is
written.
17 writefinal File to which solution at last step in sweep is
written.


If you were doing a parametric sweep of dc analyses, then readns/write would
help, but would be slower than doing a dc sweep directly.

Regards,

Andrew.
--
Andrew Beckett
Principal European Technology Leader
Cadence Design Systems, UK.