"Standard parts" for rf amps?

[John Devereux]

"RST Engineering \(jw\)" <jim@rstengineering.com> writes:

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

 

[Winfield Hill]

jw\ wrote...

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

 

[Roy Lewallen]

RST Engineering (jw) wrote:

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

 

[Henry Kiefer]

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...

"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!

 

[Henry Kiefer]

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...

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

 

[Henry Kiefer]

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...

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

 

[Henry Kiefer]

"Chris Jones" <lugnut808@nospam.yahoo.com> schrieb im Newsbeitrag
news:11o77g69er67g06@corp.supernews.com...

FastHenry, though these consider inductive and capacitive effects
I like FastHenry

- Henry

 

[RST Engineering (jw)]

"Henry Kiefer" <otc_friend@gmx.net> wrote in message
news:4384c9b8$0$27885$9b4e6d93@newsread4.arcor-online.net...

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.

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

since I was 12 years old

8 years old.

and that is 25 years back.

54 years back.

I have for example a
patent application made

I've got a few more.

and worked in the communication industry.

38 years straight now.


So you can

surely think I know what I'm doing.

Then answer the question.

Jim

 

[Winfield Hill]

jw\ wrote...

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.

BTW: I cannot understand why you're so aggressive ...

Indeed.

Then answer the question.

Answered repeatedly already.


--
Thanks,
- Win

 

[JeffM]

Mark wrote [WITHOUT CONTEXT]:

there are lots of parts...

http://groups.google.com/group/sci.electronics.design/browse_frm/thread/1e72eb22780bfcee/6939ac83d77b8ded?q=don't-click-the-reply-link-that-is-in-plain-sight+To-get-context-the-easy-way+on-Google+zzz+show-options*-*-*-snip-*-*-*-*-the-automated-blockquote-*-*-*+click-THAT-Reply-link

 

[Roy Lewallen]

RST Engineering (jw) wrote:

. . .
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"

 

[Henry Kiefer]

"RST Engineering (jw)" <jim@rstengineering.com> schrieb im Newsbeitrag
news:11o9tect0adji4b@corp.supernews.com...

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.

Then answer the question.

OK - playing on:
I got nothing. There is no power supply. No antenna interaction. No thermal
noise source. You circuit is bullshit!

Maybe we have a communication problem and should drink a beer??
- Henry

 

[RST Engineering (jw)]

"Winfield Hill" <Winfield_member@newsguy.com> wrote in message
news:dm367b01hj7@drn.newsguy.com...

jw\ wrote...

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.

No, Win, the question is well formed and quite complete. Sleep off the ten
shots of Old Rammycackle and let's have the discussion when you are sober.



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.

No, Win, neither you nor I would do such a thing. But somebody who is (as
the OP posted) new to the RF world would do so without a second thought.
You and I have been playing this game all our lives and take self-resonance
into account without even thinking about it. However, a student new to the
field (as my freshman engineering students are) makes the mistake
repeatedly, even when using a decent text called ... um ... The Art Of
Something Or Other. When their RF amplifier starts squeeging or
motorboating, I tell them that the power supply isn't bypassed well enough,
and I'll be damned if the first thing they do is put a BIGGER capacitor on
the supply line.

I'll then ask them what they think the bypass impedance is and get the stock
answer "1/(2*pi*f*c)". Hm, says I, how about the three inches of wire
between the capacitor and the supply line. Oh, says them, that's a direct
short. Straight wire doesn't have a reactive component. Hm, says I, let's
see what the network analyzer says about that. Hm, says student, it says 60
nanohenries. How can that be? Mm, 20 nanohenries per inch for #20 wire
sounds about right, so what does that series circuit look like? Hm.
Inductive at the frequency of interest. Now, grasshopper, tell me about
self-resonance of capacitors with long leads.




And

we certainly wouldn't use an inch of pcb trace unless it was
field-controlled with a ground plane.

That's not always an option in commercial gear, Win.



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.

If I didn't say what the ground is, then we can assume that I formulated the
question without ground plane. 99% of the commercial products run this way.

Sorry, jw\, but that's the way it is.

Sorry, Win, that's NOT the real world.

Jim

 

[John Larkin]

On Wed, 23 Nov 2005 15:05:42 -0800, "RST Engineering \(jw\)"
<jim@rstengineering.com> wrote:

"Henry Kiefer" <otc_friend@gmx.net> wrote in message
news:4384c9b8$0$27885$9b4e6d93@newsread4.arcor-online.net...
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.

The question is unclear. Any component must have a return path, either
when you measure it or when you use it in a circuit. The entire loop
determines the "lead" inductance. If I solder an axial cap, with 1" of
extra leads, onto the end of a hunk of coax, and analyze it with a VNA
or TDR, I can bend the cap leads into various fat/flat loops and push
the L all over the place.

John

 

[Henry Kiefer]

And why, Jim, you don't comment my effort?

Maybe I'm newer to rf as you but where is the difference between a
microprocessor decoupling from the power supply at 100MegHz and a rf stage
at the same frequency? Truly the cpu is more challenging because of the
broad used spectrum above 100MegHz.

Done PowerPC, PCI stuff and others....

- Henry

 

[Chris Jones]

RST Engineering (jw) wrote:

"Winfield Hill" <Winfield_member@newsguy.com> wrote in message
news:dm367b01hj7@drn.newsguy.com...

jw\ wrote...

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.

No, Win, the question is well formed and quite complete. Sleep off the
ten shots of Old Rammycackle and let's have the discussion when you are
sober.

It is not a complete question. You could get all sorts of different
parasitic inductance values by putting the component near or far from other
metallic objects, which usually occurs to some extent in any practical
situation. Many other things will affect the answer.

You have not yet supplied anything other than a single dimension measurement
for the component. If you want the inductance, skin effect, etc. then you
would have to give me a dimensioned drawing showing the placement of the
wires, the plating material, plating thickness and the internal
construction of the capacitor. (You would also have to pay me enough to
make it worth me bothering to simulate it.) Your question is 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.

No, Win, neither you nor I would do such a thing. But somebody who is (as
the OP posted) new to the RF world would do so without a second thought.
You and I have been playing this game all our lives and take
self-resonance
into account without even thinking about it. However, a student new to
the field (as my freshman engineering students are) makes the mistake
repeatedly, even when using a decent text called ... um ... The Art Of
Something Or Other. When their RF amplifier starts squeeging or
motorboating, I tell them that the power supply isn't bypassed well
enough, and I'll be damned if the first thing they do is put a BIGGER
capacitor on the supply line.

I'll then ask them what they think the bypass impedance is and get the
stock
answer "1/(2*pi*f*c)". Hm, says I, how about the three inches of wire
between the capacitor and the supply line. Oh, says them, that's a direct
short. Straight wire doesn't have a reactive component. Hm, says I,
let's
see what the network analyzer says about that. Hm, says student, it says
60
nanohenries. How can that be? Mm, 20 nanohenries per inch for #20 wire
sounds about right, so what does that series circuit look like? Hm.
Inductive at the frequency of interest. Now, grasshopper, tell me about
self-resonance of capacitors with long leads.




And
we certainly wouldn't use an inch of pcb trace unless it was
field-controlled with a ground plane.

That's not always an option in commercial gear, Win.
Well as you have not specified whether this is "commercial gear" and what

type of PCB material, dielectric thickness, trace width etc. of course we
can't tell you the answer. Neither could a guy who was going to answer
your question by building one and measuring it. He could find one possible
answer but there are lots of possible answers which differ because you have
not given us a complete problem to solve.

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.


If I didn't say what the ground is, then we can assume that I formulated
the
question without ground plane. 99% of the commercial products run this
way.
You still gave insufficient information on the wire geometry. I would

refute your claim that 99% of commercial products don't use a ground plane.
The cell-phone market is in the high hundreds of millions of units this
year, and is likely to reach 1 billion units per year next year, and I
guarantee you that every one will contain a multi-layer PCB with ground
planes and microstrip traces etc. every one of them designed using field
simulators and some version of SPICE to model the integrated circuit
packages and bondwires, as well as the antenna. I don't believe that this
one billion units would fit into the 1% minority of products that you think
have ground planes!

Sorry, jw\, but that's the way it is.

Sorry, Win, that's NOT the real world.

Jim

Anyhow, until you tell me how long a piece of string is, (to the nearest
micron or micro-inch whichever you prefer), I have had enough of this
thread.

Chris

 

[Martin]

Am Thu, 24 Nov 2005 09:55:13 -0800 schrieb RST Engineering (jw)
<jim@rstengineering.com>:

into account without even thinking about it. However, a student new to
the
field (as my freshman engineering students are) makes the mistake
repeatedly, even when using a decent text called ... um ... The Art Of
Something Or Other. When their RF amplifier starts squeeging or
motorboating, I tell them that the power supply isn't bypassed well
enough,
and I'll be damned if the first thing they do is put a BIGGER capacitor
on
the supply line.

Like some of us could lough nicely, when a new guy at a customer

(semiconductor fab/asics) of the last company I worked for had to test an
RF Chip. Another engineer came to look what the guy is doing, saw he
didn't bypass the power supply and recommended to do so. The young
engineer put a nice 2200ľF electrolytic at the terminals of the
lab-power-supply.



--
Martin

 

[Andy Cowley]

RST Engineering wrote:

Well, just for starters, what does Spice say about a 1000 pf capacitor with
either ˝" lead lengths or a total of 1" of PCB trace at 150 MHz.?

It's an inductor? ;-)

No such thing as a capacitor, or an inductor
or resistor for that matter. They all have
to be modelled as networks with L C and R
don't they?

vy 73

Andy, M1EBV

 

[Andy Cowley]

Henry Kiefer wrote:

To come back to your question: Spice will give you better results than your
real circuit!

Worked much DX with Spice, have you?

IMHO if the results from spice differ from the
real results then spice is wrong.

BTW have you got a realistic model for the
self-capacitance of an inductor? Can you
predict the self resonance within 5%?


vy 73

Andy, M1EBV

 

[Andy Cowley]

RST Engineering (jw) wrote:

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.

Try them on a toroidal inductor, even at HF. I have good reason to
believe they won't have anything like a model to predict self
capacitance/resonance.

vy 73

Andy, M1EBV