Question about Ansoft Designer Models - RF Cafe Forums
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Post subject: Question about Ansoft Designer Models Posted:
Tue Aug 23, 2005 7:06 pm
Joined: 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 lying around.
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.
However, when I use
the BFP620, with a 70GHz fT, the simulations fly through the transient
analysis in no time and produce nearly perfect results.
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
Any comments or help would be appreciated.
Post subject: OscillatorPosted:
Tue Aug 23, 2005 7:27 pm
What simulator are you using? Whose
models are you using?
Assuming that 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 power supplies.
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,
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
Joined: Fri Sep 02, 2005 7:25 pm
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.