U
Uwe Hercksen
FR4 can be used at 20 GHz, depending on what you're trying to do.
Hello,
well, if the transmission line is very, very short.....
bye
FR4 can be used at 20 GHz, depending on what you're trying to do.
Again, I'm looking for a diagram like frequency (some MHz to 10 GHz for
example) versus loss tangent and / or epsilon R for FR4 or other usual
PCB
material. I only found a poor black-and-white copy from 1991 in a paper
which I searched with Google. I wouldn't have thought it to be so hardto
find a graph but as noone replied to my previous question so far it does
seem to be hard!
at 100+dB isolation among traces, you do have to be pretty careful,
even at "low" frequencies.
Cheers,
Tom- Hide quoted text -
- Show quoted text -
I do stuff down to a few ps RMS jitter on a regular 6 or 8-layer
board, microstrip traces, with switching supplies and uPs and display
drivers on the same board. Picoseconds aren't tough these days.
John- Hide quoted text -
- Show quoted text -
John Larkin said:But FR-4 varies a lot, so there's no definitive data.
What are you trying to do?
____________________________________
You are hoping that we believe switchers
cause lots of noise ....
Zero ripple is what switchers do !
The sudden pulse of current is only
around a very short loop , it does
not cause noise .
They dont even have "ground loops"
BTW
Study CAT5e Ethernet cable .
garbage !
USB cables are much faster .
I think ppl limit themselves to
whats avail in PCB , then complain
when it dont work , but if they'd
experiment , they'd find the problem
is using thin PCB .
Then they limit on putting down
100 transmission lines per mm .
You cant learn , unless you experiment.
Sending signals that will be amplified
use high Z ( ~65 ohms ) and
sending power needs low Z .
These rules can't be bent .
Thats what you're doin , is bending
rules ...
Grant Edwards said:BTW
Study CAT5e Ethernet cable .
garbage !
USB cables are much faster .
I think ppl limit themselves to
whats avail in PCB , then complain
when it dont work , but if they'd
experiment , they'd find the problem
is using thin PCB .
Then they limit on putting down
100 transmission lines per mm .
You cant learn , unless you experiment.
Shite man, what are you using for a computer, a 40-column
Commodore PET?
[...]
Sending signals that will be amplified
use high Z ( ~65 ohms ) and
sending power needs low Z .
These rules can't be bent .
Thats what you're doin , is bending
rules ...
Even a PET wouldn't explain the random indentation.
Hi John, I'm trying to compare several loss tangent values (I think that's
the decisive parameter..!?) from several materials, FR4-, PE, etc. over the
frequency. But it's hard to find such diagrams.
Grant Edwards said:BTW
Study CAT5e Ethernet cable .
garbage !
USB cables are much faster .
I think ppl limit themselves to
whats avail in PCB , then complain
when it dont work , but if they'd
experiment , they'd find the problem
is using thin PCB .
Then they limit on putting down
100 transmission lines per mm .
You cant learn , unless you experiment.
Shite man, what are you using for a computer, a 40-column
Commodore PET?
[...]
Sending signals that will be amplified
use high Z ( ~65 ohms ) and
sending power needs low Z .
These rules can't be bent .
Thats what you're doin , is bending
rules ...
Even a PET wouldn't explain the random indentation.
And the random word and punctuation spacing. Some kind of mobile
phone? The Microsoft Word Usenet Export Filter?
I think it's the usenet equivalent of green ink.
<http://en.wikipedia.org/wiki/Green_ink>
In coax for 2.5 Ghz , for example ,
it WILL have a large diameter and
the center will have an exact dia and
ratio .. No substitutes .
____________________________________
You are hoping that we believe switchers
cause lots of noise ....
Zero ripple is what switchers do !
The sudden pulse of current is only
around a very short loop , it does
not cause noise .
They dont even have "ground loops"
John Larkin said:No, what are you trying to *do*? WHY do you want a "coax on a pc
board"?
Ah, okay, what I am actually trying to find out is what makes FR4 act worse
than e.g. teflon at data rates beyond 2,5 Gbps. Is it the loss tangent or
the epsilon r? How is the frequency-dependent attenuation physically
describable? Where does the energy go? Heat, ...? It was my opinion that
higher frequencies can be transmitted over coax but not over FR4 because of
the geometry. Because in a coax there is (almost) no energy loss because the
TEM wave is "captured" by the outer shield and in a planar setup like
stripline or microstrip there are E-field and H-field lines vanish into the
air environment (or somewhere else...). Therefore I'm trying to design a
coax on a PCB. Am I right with my thoughts, anyway?
John said:Please post the schematic of a zero-ripple switcher.
John
Michael said:Sorry, but that feature is only available on the 0 volt model.
John said:.... snip ...
Please post the schematic of a zero-ripple switcher.
Indeed there are the topologies of the switchers with exactly zero or
almost zero ripple, assuming the ideal symmetry of everything.
John said:Like a polyphase switcher with *big* inductors?
But I don't want "almost zero ripple", I want the real thing.