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From: firstname.lastname@example.org (carltons)
Subject: Re: Modelling of Chip Resistors at 2.4GHz
User-Agent: NewsWatcher-X 2.2.3b2
NNTP-Posting-Date: Sun, 13 Oct 2002 02:01:37 GMT
Date: Sun, 13 Oct 2002 02:01:37 GMT
In article , John Larkin
> On Sat, 12 Oct 2002 09:05:39 GMT, email@example.com (carltons) wrote:
> >Does anyone know of a source of information about the model for a standard
> >chip resistor such as a 1206 or 2512 resistor at a value of around 100 ohm
> >at 2.4GHz?
> >I'm not talking about the microwave type, but just the plain jane Koa,
> >Panasonic, etc. resistor that we normally use.
> >Thanks for any help.
> >Steve WB4CZR
> Rough guess for a 1206: 1 nH + 0.2 pf. So it's mainly R+L at a couple
> of GHz, and actually a pretty good resistor.
> One other issue is the problem of making connections. If a circuit
> board trace is just the width of the resistor, and maybe the other
> side of the resistor is a big ground sheet (say, for a termination)
> things are pretty good. But if a wide trace ends in a skinny part, the
> inductance goes up. A decent termination for a 0.1" wide, 50 ohm trace
> is three 150-ohm 0603 resistors in parallel, spread across the trace
> width. So paralleled 1206s might be better than a single 2512. Or use
> a single 1206; soldered to wide traces, it can stand well above its
> rated power dissipation.
Thanks guys. I would have guessed about 0.7 nH John, but we're both close
to one another on this. I've been having this argument going with a
fellow engineer involving the 100 ohm resistor (1206) used in one of our
splitter/combiners. I contend that we use a 2512 since it would quarter
the shunt C of the part and lower the inductance at the same time. I also
have seen some data on the web (I don't remember where but it was from one
of the big vendors) that the effective resistance of the standard resistor
at 2.4 GHz is about 60% of its low frequency value due to shunt C. I
can't really see a big increase in R due to skin effect even at 2.4 GHz
since most of the resistors are so thin to begin with and have the correct
shape to compensate anyhow. BTW, the 2512 would also be about the same
width of the microstrip now in the combiner's Zo lines which should also
be desirable. I have also come up with a configuration change which could
make all of this less sensitive to the parasitics of the resistor, but I
would still like to know what to use as a resistor model for any freq up
Problem: We have old equipment and it's hard to measure S11 with
reliability. We don't have any fancy design tools like Sonnet or
Eagleware. What we both agree on is the fact that the layout does affect
the performance of anything we put in there. I wish I had a HP8753D and a
decent fixture, not to mention the cal kit. (I'm dreaming again)
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