| Author |
Message |
Henry Kiefer
Guest
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 Posted:
Thu Nov 24, 2005 9:35 am Post subject:
Re: "Standard parts" for rf amps? |
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"RST Engineering (jw)" <jim@rstengineering.com> schrieb im Newsbeitrag
news:11o9tect0adji4b@corp.supernews.com...
| Quote: | 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
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RST Engineering (jw)
Guest
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| Posted:
Thu Nov 24, 2005 11:55 pm Post subject:
Re: "Standard parts" for rf amps? |
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"Winfield Hill" <Winfield_member@newsguy.com> wrote in message
news:dm367b01hj7@drn.newsguy.com...
| Quote: | 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
| Quote: | 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
| Quote: | 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
| Quote: | 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.
| Quote: | Sorry, jw\, but that's the way it is.
|
Sorry, Win, that's NOT the real world.
Jim |
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John Larkin
Guest
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| Posted:
Fri Nov 25, 2005 12:20 am Post subject:
Re: "Standard parts" for rf amps? |
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On Wed, 23 Nov 2005 15:05:42 -0800, "RST Engineering \(jw\)"
<jim@rstengineering.com> wrote:
| Quote: |
"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
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Henry Kiefer
Guest
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| Posted:
Sun Nov 27, 2005 1:35 am Post subject:
Re: "Standard parts" for rf amps? |
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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 |
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Chris Jones
Guest
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| Posted:
Sun Nov 27, 2005 1:35 am Post subject:
Re: "Standard parts" for rf amps? |
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RST Engineering (jw) wrote:
| Quote: |
"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.
| Quote: | 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.
| Quote: | 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!
| Quote: | 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 |
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Martin
Guest
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| Posted:
Sun Nov 27, 2005 9:35 am Post subject:
Re: "Standard parts" for rf amps? |
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Am Thu, 24 Nov 2005 09:55:13 -0800 schrieb RST Engineering (jw)
<jim@rstengineering.com>:
| Quote: | 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 2200µF electrolytic at the terminals of the
lab-power-supply.
--
Martin |
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Andy Cowley
Guest
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| Posted:
Mon Dec 05, 2005 5:35 pm Post subject:
Re: "Standard parts" for rf amps? |
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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.
|
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 |
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Jim Thompson
Guest
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| Posted:
Mon Dec 05, 2005 5:35 pm Post subject:
Re: "Standard parts" for rf amps? |
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On Mon, 5 Dec 2005 17:14:15 GMT, Andy Cowley <andy.cowley@uwe.ac.uk>
wrote:
| Quote: | 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
|
Model making is driven by need. 1nF capacitors don't exist on-chip
(at least not very often :), so I don't have a model. But I have
built a model of a wirebond that is good up into the 3GHz range.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food. |
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Andy Cowley
Guest
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| Posted:
Mon Dec 05, 2005 5:35 pm Post subject:
Re: "Standard parts" for rf amps? |
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Henry Kiefer wrote:
| Quote: | 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 |
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Andy Cowley
Guest
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| Posted:
Mon Dec 05, 2005 5:35 pm Post subject:
Re: "Standard parts" for rf amps? |
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RST Engineering 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.?
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 |
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Roy Lewallen
Guest
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| Posted:
Tue Dec 06, 2005 1:35 am Post subject:
Re: "Standard parts" for rf amps? |
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Andy Cowley wrote:
| Quote: | . . .
IMHO if the results from spice differ from the
real results then spice is wrong.
. . .
|
If the results from SPICE differ from the real results, then your model
is inadequate.
Roy Lewallen, W7EL |
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Jim Thompson
Guest
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| Posted:
Tue Dec 06, 2005 1:36 am Post subject:
Re: "Standard parts" for rf amps? |
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On Mon, 5 Dec 2005 23:53:38 +0100, "Henry Kiefer" <otc_friend@gmx.net>
wrote:
| Quote: | Spice is as good as the input is!
Spice is not a Maxwell field equations solver!
You can predict within 5% without Spice?? How?
- Henry
[snip] |
Some of us have done better than 5% prediction BC (before CAD)... like
for close to 20 years before I ever saw a computer... and 25 years
before simulation software.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food. |
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Henry Kiefer
Guest
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| Posted:
Tue Dec 06, 2005 1:36 am Post subject:
Re: "Standard parts" for rf amps? |
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Spice is as good as the input is!
Spice is not a Maxwell field equations solver!
You can predict within 5% without Spice?? How?
- Henry
"Andy Cowley" <andy.cowley@uwe.ac.uk> schrieb im Newsbeitrag
news:Ir1Aq8.E8q@bath.ac.uk...
| Quote: | 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 |
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Henry Kiefer
Guest
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| Posted:
Tue Dec 06, 2005 5:35 pm Post subject:
Re: "Standard parts" for rf amps? |
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Sure Jim. I understand you. That was the time where time was cheaper. Once I
programmed a Gauss linear equations system solver on my Casio FX-602P -
having 512 bytes and even left one byte (for extensions ;-) It was with
minimal input help system (Showing the indices to input) and the matrix was
of dynamical order. (Sorry for my bad english)
I can buy resistors and capacitors with 5%, sometimes with 1%. If you build
a rc oscillator with 1% component values, you get an error typical 1,5%. And
then you add the active components with horrible semiconductor strayung
values. Of course, it is possible with feedback structures to linearize and
stabilize such systems.
So, where is the difference between measurement of the component values and
calculating by hand the circuit OR setting the measured values in the Spice
component dialog boxes? The difference is the time needed and the
possibility to make errors.
5% is a real good value for an analog system.
Hey Jim - Why you don't answer my second private message? :-(
- Henry
"Jim Thompson" <To-Email-Use-The-Envelope-Icon@My-Web-Site.com> schrieb im
Newsbeitrag news:dej9p1te7qiapphldsgvm3toip0usmeih9@4ax.com...
| Quote: | On Mon, 5 Dec 2005 23:53:38 +0100, "Henry Kiefer" <otc_friend@gmx.net
wrote:
Spice is as good as the input is!
Spice is not a Maxwell field equations solver!
You can predict within 5% without Spice?? How?
- Henry
[snip]
Some of us have done better than 5% prediction BC (before CAD)... like
for close to 20 years before I ever saw a computer... and 25 years
before simulation software.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food. |
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Saandy , 4Z5KS
Guest
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| Posted:
Wed Dec 07, 2005 3:35 pm Post subject:
Re: "Standard parts" for rf amps? |
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The NE85633 bipolar transistor from California Eastern Laboratories
(CEL) ! very cheap quite stable and with a good noise figure. very well
documented by the manufacturer!
try to fish a development kit of SMD coils from Murata, sometimes they
give them away for free.
I personally prefer to go with air wound inductors, they're better and
quite small at these frequencies.
Saandy 4Z5KS |
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