Question About Ansoft Designer Models - RF Cafe Forums
Post subject: Question about Ansoft Designer Models
Posted: Tue Aug 23, 2005 7:06 pm
Tue Aug 23, 2005 6:33 pm
Hello everyone. I'm new
to the forum and like what I have browsed so far.
In a nutshell,
I'm designing a 480MHz square-wave oscillator circuit somewhat resembling
PECL logic with the inclusion of a T-Line for delay and was planning
to use the Infineon BFP405 due to its high 25GHz fT, I have used
it previously in other amplifier circuits, and I still have a few
When analyzing in the frequency domain, everything
is great, but for the square-wave design, I have been using the
transient analysis in the time-domain and have found that the simulations
take forever and I get horrible ringing in the output.
when I use the BFP620, with a 70GHz fT, the simulations fly through
the transient analysis in no time and produce nearly perfect results.
The BFP620s seem hard to come by and I don't want to waste
time building this circuit and have it perform horribly due to some
overly simplistic model, but I also cannot spend 20min waiting for
each new simulation run with the BFP405 only to get the ringing.
By the way, I am taking into account and testing different termination
techniques on the T-Line.
Any comments or help would be appreciated.
OscillatorPosted: Tue Aug 23, 2005 7:27 pm
are you using? Whose models are you using?
you're using SPICE, the standard versions generally take a long
time to simulate oscillators in particular - and it's made worse
by inadequate vendor models. And you really have to model your own
parasitics - no way around that!
Even though it's not aimed
at your application, an example of a version of SPICE that's been
optimized for oscillators is Linear Technology's SwitcherCAD/LTSpice.
They've gone in and set the various parameters that most users don't
even know about, in order to get fast simulation for their switching
If you've got the '405 amplifiers on hand,
maybe prototyping would be a good approach - if you have the necessary
instruments. (You'll want them for the final product verification,
Post subject: Posted: Wed Aug 24, 2005 11:39 am
Joined: Tue Aug 23, 2005 6:33 pm
I'm using Ansoft
Designer and the associated models that come with it.
Post subject: Posted: Tue Oct 25,
2005 8:10 am
Joined: Fri Sep 02, 2005
Location: Hampshire UK
I can attest
to the SWCAD speed. I used it to check out how far one could press
things with a two-FET symmetrical oscillator which I knew would
start, but simulation attempts were failing. The SWCAD ran straight
off, and allowed me to sim the first few microseconds (startup)
at 670MHz. Also - its free!
It has to be said that it does
not come with easy bells and whistles if you want to put in any
models it did not come with. You have to get down and dirty with
the netlist file.