SPICE models for big fat RF transistors

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Hello Newsgroup,

Does anyone know where to get models for the really big fat base station
transistors? Right now it doesn't matter which mfg. NXP doesn't seem to
have one for the BLF878 anymore, somehow gone, I'll have to ask where it
went. Anyhow, they only provide scant information and only at particular
bias points, like these:

http://www.nxp.com/models/spicespar/BLF548.html

I need something real, something I can plug into LTSpice.

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: SPICE models for big fat RF transistors

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Why?  Did something go *Phut* again ?:-)

                                        ...Jim Thompson
--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Re: SPICE models for big fat RF transistors
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No, but I want to make sure it's all kosher because a *phut* situation
could become rather ugly if you combine a dozen of those. Molten solder
splattering about, blaring sirens ...

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: SPICE models for big fat RF transistors
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So, guys, got an answer from NXP: They do not create SPICE models for
their RF products. They only create ADS models.

I assume ADS only works with EEsof which probably still costs the
equivalent of a nice car and I bet models are not convertible. Great.
Cuts off much of the secondary users for their RF transistors. What were
they thinking?

Oh, and the support email says you cannot reply to the message. Oh man,
now that they've got their web site in order it starts to crumble
somewhere else.

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: SPICE models for big fat RF transistors

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Sounds like it's a Curtice model... works in PSpice ;-)

                                        ...Jim Thompson
--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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But LTSpice wants LGATE, RGATE, CG, CRSS, CISS, LS, CS ... and so on :-(

I plan to use it in a quite unorthodox application (like usual ...).

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: SPICE models for big fat RF transistors

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I would guess someone here with an IEEE membership can locate a
translator.

(The Curtice model is built into PSpice... primary use: GaAs FET's)

                                        ...Jim Thompson
--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Re: SPICE models for big fat RF transistors
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I am a member but they nickel and dime you for access to just about
everything not in your subscribed societies, so probably no access to
what's needed. But thanks for the info, gives me pointers how to search
on the web.


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Somehow it doesn't look like the Curtice model on page 8-103 of this
Agilent doc though:

http://www.ece.uci.edu/eceware/ads_docs/pdf/netlist.pdf

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: SPICE models for big fat RF transistors
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think I have seen somewhere (yahoo forum?) that someone got a model
like
that into ltspice but it wouldn't work for transient analysis.

what kind of transistor specs are you looking for?, I've seen models
for other
big rf transistors that work in lspice somewhere.

-Lasse

Re: SPICE models for big fat RF transistors
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Haven't found anything there but will keep looking elsewhere. However,
transient analysis is exactly what I am after, I am not using it as a
regular RF amp.


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As big a honking RF power transistor as possible, good up to a GHz, or
at least lower UHF. I am prepared to live with whatever specs they've
got, pretty slim pickens up there anyhow because the market for this
stuff is small. But I'd need a somewhat proper SPICE model. This kind of
circuitry has to be simulated pretty well, trying it all on the bench
can lead to lots of molten solder splattering around, a loud bang,
smoke, ferrite pieces flying all over the place and so on.


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Yes, PolyFet has some but this looks like high-price specialty parts. I
was hoping for a more mainstream part from a bis semi mfg.

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: SPICE models for big fat RF transistors


Joerg, I don't understand what the problem is.

The parameters for Advanced_Curtice2 model are available - all you
have to do is enter them as a text field.

But, if you need some BIG models for RF transistors,
you can try:

freescale website

Most of the GaN sites (Nirronix, Cree) have models
but they are in  ADS format.

HTH,
dave

Re: SPICE models for big fat RF transistors
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Ok, I'll try again but NXP told me you can't, only works for ADS.


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But AFAIK nothing above 50W. PolyFet has bigger ones though and much
better model support than NXP.

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: SPICE models for big fat RF transistors


Joerg, OK now I know a little bit more of what you are
looking for.

What frequency range are you looking for?

Freescale has some LDMOS chips in the
500 - 1500 MHz range.

Cree and Nitronex have GaN chips which
use the MCM SPICE models

Dave

Re: SPICE models for big fat RF transistors
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Devices that can do up to lower UHF, 500MHz or so, with decent
efficiency would be fine. Tons of power ;-)


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Yes, but even the Nitronex flagship NPT1007 can only do around 100W. I
am looking for something that can stomach a few hundred watts. PolyFet
has one, not quite like the big BLF but close and at least they give out
SPICE parameters.

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: SPICE models for big fat RF transistors


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I looked into that some years ago when I still was interested in
fat RF transistors and the consensus was that Spice doesn't cut it
for this application. There were models from Moto/Freescale/On/MaCom
and Philips/NXP, but only for ADS, Microwave Office and Harbec/Genesys/Eagleware
(that is now Agilent, too). These simulators had been specially
enhanced to digest these models. IIRC it was a real physics problem,
maybe local themal effects.

Sorry, that means $$$.


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regards, Gerhard

Re: SPICE models for big fat RF transistors
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Harbec/Genesys/Eagleware
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Actually about an hour ago I simulated the first such power transistor,
a 300W VHF device from PolyFet because they furnish a fairly elaborate
SPICE model. It is a subcircuit with three different semiconductor
models and numerous discretes in there. So far it shows all the nasties
you see with VHF broadband stuff in the real world, meaning it can't be
too far from the real world. I have designed lots of power pulsers in my
life, all under 15nsec though and it seems that going to 5nsec make the
unwanted stuff grow 10x :-(


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Yep, and that's not (yet) in the budget for this project. Also, those
simulators are geared towards RF stages that run continuous duty. Mine
will be pulsed pretty brutally, so hardcore time domain sims are needed.

Now I am trying to figure out a VSWR protection that acts within a few
nanoseconds ...

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: SPICE models for big fat RF transistors

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IIRC, these fat FETs had a memory effect, i.e. they behaved differently
wrt what happened some us/ms before.


G.

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There are some local heating issues, definitely at the power level I am
dealing with. But it could be worse: The old BJTs had sort of a ROM
effect. Treat them too harshly and one of more of the emitter paths
would go phsst ... *phut* ... and then your transistor would deliver
only half the power from here on. Forever, it would not fix itself
anymore. I've used such a partially damaged transistor that was down to
60% of nominal in a 2m transceiver for over a decade, that used one was
all my student's budget would allow (dipping into the beer budget was
not an option ...).

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: SPICE models for big fat RF transistors
On Sun, 19 Jul 2009 00:09:09 +0200, Gerhard Hoffmann

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That sounds a lot like what some might call thermal inertial.  Of
course you might want to model it as a thermal array device to get
closer to the actual operating physics.

Re: SPICE models for big fat RF transistors

Joerg,

You might to reconsider the decision to build a switch to measure
VSWR.

You might want to look at gradually decreasing power as the VSWR goes
up.
If you switch everything at once, you will have a very large arc as
the power has to
go somewhere ( usually a place that you don't want it to)
There are companies out there that make VSWR protection circuits but
they
have be integrated into the PA in some fashion.

Just my $0.02,
Dave


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