| Author |
Message |
Joel Kolstad
Guest
|
 Posted:
Wed Nov 23, 2005 8:02 am Post subject:
Re: "Standard parts" for rf amps? |
|
|
"Joel Kolstad" <JKolstad71HatesSpam@yahoo.com> wrote in message
news:11o7iv99ppgmsca@corp.supernews.com...
| Quote: | For some of the university work I've done, some of our reference papers are
from people modeling power lines as full-fledged transmission lines that are
many wavelengths long at 50Hz. No simple equivalent circuit model works for
them either!
|
OK, I did get a little over-excited there -- it should say "that are
significant fractions of a wavelength long," (e.g., more than 1/6th) such that
you can't use a simple circuit model for them.
|
|
| Back to top |
|
 |
John Larkin
Guest
|
| Posted:
Wed Nov 23, 2005 8:12 am Post subject:
Re: "Standard parts" for rf amps? |
|
|
On Mon, 21 Nov 2005 23:55:26 -0800, "RST Engineering"
<jim@rstengineering.com> wrote:
| Quote: | Well, just for starters, what does Spice say about a 1000 pf capacitor with
either ½" lead lengths or a total of 1" of PCB trace at 150 MHz.?
Jim
|
When they matter, just poke in the appropriate series L or a bit of
transmission line. I use Spice now and then to sim picosecond stuff.
Even if the simulation isn't highly accurate, it helps train your
instincts, shows you which parasitics will have which effects, so when
you build the real thing you have a jump on the complexity.
Hell, 150 MHz is slow.
John |
|
| Back to top |
|
|
John Larkin
Guest
|
| Posted:
Wed Nov 23, 2005 8:14 am Post subject:
Re: "Standard parts" for rf amps? |
|
|
On Tue, 22 Nov 2005 10:05:02 -0800, "RST Engineering"
<jim@rstengineering.com> wrote:
| Quote: |
"Henry Kiefer" <otc_friend@gmx.net> wrote in message
news:4382ffe2$0$27884$9b4e6d93@newsread4.arcor-online.net...
Ok Jim. You're asked about the stray components hidden in the real
parts/circuit.
There is nothing hidden at all. Strays are a part of the real life at VHF
and above. Sometimes strays have more effect than the part itself.
If you take the values from the datasheets for die and/or
package or give it a guess if not available, and add values for the pcb
lines, you have a good simulation result.
Horsefeathers. What "values" do you add for the pcb lines?
|
Lumped L and C if things are slow, or a hunk of transmission line when
things get fast. Works fine.
John
|
|
| Back to top |
|
|
Roy Lewallen
Guest
|
| Posted:
Wed Nov 23, 2005 8:37 am Post subject:
Re: "Standard parts" for rf amps? |
|
|
Joel Kolstad wrote:
| Quote: | "Joel Kolstad" <JKolstad71HatesSpam@yahoo.com> wrote in message
news:11o7iv99ppgmsca@corp.supernews.com...
For some of the university work I've done, some of our reference papers are
from people modeling power lines as full-fledged transmission lines that are
many wavelengths long at 50Hz. No simple equivalent circuit model works for
them either!
OK, I did get a little over-excited there -- it should say "that are
significant fractions of a wavelength long," (e.g., more than 1/6th) such that
you can't use a simple circuit model for them.
|
That's interesting -- SPICE has models for (lossless) transmission
lines, and lines of that length can also be adequately modeled with a
few LC sections. I can imagine line loss could be tricky, though. I've
modeled skin effect loss in the process of designing time-domain
circuits to compensate for delay line loss over a wide time range (and
therefore broad frequency range). But loss due to interaction of the
fields with ground underneath the wires might be more difficult. At
least you've only got one frequency to deal with -- unless harmonic
content is high enough to worry about. Perhaps you've also got to deal
with loss due to radiation?
Roy Lewallen, W7EL |
|
| Back to top |
|
|
RST Engineering (jw)
Guest
|
| Posted:
Wed Nov 23, 2005 9:35 am Post subject:
Re: "Standard parts" for rf amps? |
|
|
Agreed, John, 150 MHz is damned near DC for a lot of us, but as yet I have
no answer from the "spice" folks for the 1 nf capacitor question. A lot of
fancydancing but no answers.
Jim
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:dpj7o19ch3ekfq6c1ekhnr65iouq76trrk@4ax.com...
| Quote: | On Mon, 21 Nov 2005 23:55:26 -0800, "RST Engineering"
jim@rstengineering.com> wrote:
Well, just for starters, what does Spice say about a 1000 pf capacitor
with
either ½" lead lengths or a total of 1" of PCB trace at 150 MHz.?
Jim
When they matter, just poke in the appropriate series L or a bit of
transmission line. I use Spice now and then to sim picosecond stuff.
Even if the simulation isn't highly accurate, it helps train your
instincts, shows you which parasitics will have which effects, so when
you build the real thing you have a jump on the complexity.
Hell, 150 MHz is slow.
John
|
|
|
| Back to top |
|
|
John Devereux
Guest
|
| Posted:
Wed Nov 23, 2005 3:43 pm Post subject:
Re: "Standard parts" for rf amps? |
|
|
"RST Engineering \(jw\)" <jim@rstengineering.com> writes:
| Quote: | Agreed, John, 150 MHz is damned near DC for a lot of us, but as yet I have
no answer from the "spice" folks for the 1 nf capacitor question. A lot of
fancydancing but no answers.
|
I am not an expert, but can you not just add a bit of series L to
approximate this? Or even transmission line for higher frequencies /
longer tracks.
I have had surprisingly good results simulating a single transistor
UHF oscillator at ~500MHz. The results agreed with reality quite well,
even *without* explicitly modelling all the parasitics. Certainly
spice was better than me at predicting what would happen (although
that is not saying much!) I guess perhaps the reason that I could get
away with this was because of the small size and high performance of
SMT parts these days.
--
John Devereux |
|
| Back to top |
|
|
Roy Lewallen
Guest
|
| Posted:
Wed Nov 23, 2005 5:35 pm Post subject:
Re: "Standard parts" for rf amps? |
|
|
RST Engineering (jw) wrote:
| Quote: | Agreed, John, 150 MHz is damned near DC for a lot of us, but as yet I have
no answer from the "spice" folks for the 1 nf capacitor question. A lot of
fancydancing but no answers.
Jim
|
I didn't realize that this question was addressed to all "'spice'
folks", but was directed only to the OP. That's probably why the
"'spice' folks" haven't leapt to respond. Anyone who uses SPICE
professionally, and indeed a great number of amateur users should be
able to answer the question easily.
At 150 MHz, a capacitor lead can generally be handled as a single lumped
inductance. The amount depends on the wire's diameter and environment,
but around 7 nH is a good working number for a half inch lead. The
inductance of the capacitor body itself might have to be included in the
model if high accuracy is important. Capacitance to ground, from both
the leads and the capacitor body, might also be important if the
impedance of the circuit to ground is high. If so, it can be included.
The way I'd approach inclusion of the C would be to calculate the
impedance and length of the transmission line comprised of the lead and
ground plane or capacitor body and ground plane, then convert those
values to a single series L and shunt C rather than just directly using
a transmission line model -- very short transmission lines in a model
can greatly slow SPICE calculations unless there are also other very
short time constants involved.
On the other hand, if the "leads" are PC traces over a ground plane,
shunt capacitance will be higher, and the approach I mentioned with the
transmission line is the way I'd always do it. The model for the leads
would include both L and C. As an example, if the "lead" is a .010"
trace on .032" FR4 material (er ~ 5) over a ground plane, it makes a
transmission line of Z0 = 105 ohms, velocity factor 0.55. The equivalent
L and C of a half inch of this line are 8 nH and 0.73 pF respectively.
Other characteristics of the capacitor such as ESR might have to be
included in the model depending on the application.
You gave a capacitor value in your question -- an ideal capacitor of
that value would of course be the other part of the model.
SPICE is used daily, as it has been for decades, by professionals and
produces strikingly good results in the hands of someone who is skilled
at modeling and has a good understanding of the circuitry being modeled.
I've personally used SPICE for modeling linear to highly nonlinear
circuits up to 50 GHz, where even tiny SMT components were often modeled
as transmission lines and every pad and solder blob is significant and
included. The results were used in the design of products which have
been successfully produced by the thousands and sold for years.
Roy Lewallen, W7EL |
|
| Back to top |
|
|
Winfield Hill
Guest
|
| Posted:
Wed Nov 23, 2005 5:35 pm Post subject:
Re: "Standard parts" for rf amps? |
|
|
jw\ wrote...
| Quote: |
Agreed, John, 150 MHz is damned near DC for a lot of us, but as
yet I have no answer from the "spice" folks for the 1 nf capacitor
question. A lot of fancydancing but no answers.
|
Spice, smice. You got good answers. Wake up, spice is just an
engine to run your component models in circuits of your making.
Once one gets beyond the "toy" level of using spice it becomes
necessary to vet and complete the models of all your critical
components, including parasitic circuit elements. Want a good
RF capacitor model, you do well to make it yourself, from the
manufacturer's data and info, and from your understanding of the
part, aided by theory and bench measurements. Then vet your model
with more bench measurements. Thinking about component leads and
PCB wiring? Hey, you need to explicitly add all these into your
circuit. Just don't blame any resulting shortcomings on "spice."
--
Thanks,
- Win |
|
| Back to top |
|
|
Henry Kiefer
Guest
|
| Posted:
Thu Nov 24, 2005 12:27 am Post subject:
Re: "Standard parts" for rf amps? |
|
|
I know of a german power line corporation who develops Spice models for
their power line test equipment. So it must be possible...
- Henry
"Joel Kolstad" <JKolstad71HatesSpam@yahoo.com> schrieb im Newsbeitrag
news:11o7iv99ppgmsca@corp.supernews.com...
| Quote: | "Ken Smith" <kensmith@green.rahul.net> wrote in message
news:dm0h2k$8hi$4@blue.rahul.net...
Heck, that can happen before you hit 1MHz. Check out the ESL and ESR of
a
47,000uF capacitor some time.
For some of the university work I've done, some of our reference papers
are
from people modeling power lines as full-fledged transmission lines that
are
many wavelengths long at 50Hz. No simple equivalent circuit model works
for
them either!
|
|
|
| Back to top |
|
|
Henry Kiefer
Guest
|
| Posted:
Thu Nov 24, 2005 1:35 am Post subject:
Re: "Standard parts" for rf amps? |
|
|
OK Jim -
I simulated your question in a first trial. Here is the result:
approx. 70MegHz resonance for 100pF, 30mOhm ESR and 5nH for the trace.
Surely I would prefer smd chips having better results.
BTW: I cannot understand why you're so aggressive and I would prefer that
the thread will go in direction of my FIRST posting. I'm doing electronics
since I was 12 years old and that is 25 years back. I have for example a
patent application made and worked in the communication industry. So you can
surely think I know what I'm doing. Thanks!
- Henry
"RST Engineering (jw)" <jim@rstengineering.com> schrieb im Newsbeitrag
news:11o82iimo8iv1d6@corp.supernews.com...
| Quote: | Agreed, John, 150 MHz is damned near DC for a lot of us, but as yet I have
no answer from the "spice" folks for the 1 nf capacitor question. A lot
of
fancydancing but no answers.
Jim |
|
|
| Back to top |
|
|
Henry Kiefer
Guest
|
| Posted:
Thu Nov 24, 2005 1:35 am Post subject:
Re: "Standard parts" for rf amps? |
|
|
You can that simulate as a rc coupled line of a few steps. That works even
for battery simulations.
- Henry
"Roy Lewallen" <w7el@eznec.com> schrieb im Newsbeitrag
news:11o7iq78697846d@corp.supernews.com...
| Quote: | Ken Smith wrote:
Heck, that can happen before you hit 1MHz. Check out the ESL and ESR of
a
47,000uF capacitor some time.
How about dielectric absorption ("soak")? I first encountered this in an
electrolytic capacitor being used for generating a sweep of about a
minute duration. The capacitor had to be kept shorted for several
seconds between sweeps in order for the charge to adequately empty, an
equivalent frequency of less than one Hz.
Roy Lewallen, W7EL |
|
|
| Back to top |
|
|
RST Engineering (jw)
Guest
|
| Posted:
Thu Nov 24, 2005 1:35 am Post subject:
Re: "Standard parts" for rf amps? |
|
|
"Henry Kiefer" <otc_friend@gmx.net> wrote in message
news:4384c9b8$0$27885$9b4e6d93@newsread4.arcor-online.net...
| Quote: | OK Jim -
I simulated your question in a first trial. Here is the result:
approx. 70MegHz resonance for 100pF, 30mOhm ESR and 5nH for the trace.
Surely I would prefer smd chips having better results.
|
But that wasn't the question. THe question was to simulate a 1000 pf (1 nf)
capacitor at 150 MHz. with an inch of lead or an inch of normal pcb trace
and tell me what you get.
| Quote: |
BTW: I cannot understand why you're so aggressive and I would prefer that
the thread will go in direction of my FIRST posting.
|
OK by me.
I'm doing electronics
| Quote: | since I was 12 years old
|
8 years old.
| Quote: | and that is 25 years back.
|
54 years back.
| Quote: | I have for example a
patent application made
|
I've got a few more.
| Quote: | and worked in the communication industry.
|
38 years straight now.
So you can
| Quote: | surely think I know what I'm doing.
|
Then answer the question.
Jim |
|
| Back to top |
|
|
Winfield Hill
Guest
|
| Posted:
Thu Nov 24, 2005 7:49 am Post subject:
Re: "Standard parts" for rf amps? |
|
|
jw\ wrote...
| Quote: |
The question was to simulate a 1000 pf (1 nf) capacitor at
150 MHz. with an inch of lead or an inch of normal pcb trace
and tell me what you get.
|
Such a question is stupid and incomplete. First of all, in
cases where impedance matters, one wouldn't dare use an inch
of lead at 150MHz, we'd cut that short, 0.1-inch max. And
we certainly wouldn't use an inch of pcb trace unless it was
field-controlled with a ground plane. This is true whether a
1nF cap is involved or not. If you were to insist on analyzing
an inch of lead, we'd insist on knowing *all* about the ground
scene. Since you aggressively put your question without any
relevant information about what the ground is like, and where
it is, the question is intrinsically-stupid and incomplete.
Sorry, jw\, but that's the way it is.
| Quote: | BTW: I cannot understand why you're so aggressive ...
|
Indeed.
| Quote: | Then answer the question.
|
Answered repeatedly already.
--
Thanks,
- Win |
|
| Back to top |
|
|
JeffM
Guest
|
|
| Back to top |
|
|
Roy Lewallen
Guest
|
| Posted:
Thu Nov 24, 2005 9:35 am Post subject:
Re: "Standard parts" for rf amps? |
|
|
RST Engineering (jw) wrote:
| Quote: | . . .
Then answer the question.
|
Did you find my answer to be inadequate or incorrect? If so, in what
ways? If not, why do you need it to be answered again?
Roy Lewallen, W7EL
-- one of the "'spice' folks" |
|
| Back to top |
|
|
|
|
|
|
FAQ
Memberlist
Register
Profile
Log in to check your private messages
Log in