Anyone have a decent Spice model for a twisted pair... lossy, not the ideal model in circulation? ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
On Sun, 08 Dec 2013 10:41:37 -0700, Jim Thompson Gave us:
using cat 5e specs and hardware and calling it cat 6 would yield lossy operation at the upper end.
There's enormous variation in twisted pairs, even among "standard" things like compliant CAT5 and CAT6 cables.
The Spice lossy delay line implements The Telegrapher's Equation, but ignores skin loss variation with frequency. The best thing to usually do is get a chunk of the actual cable of the expected length and note its step response on a scope, then fiddle the Spice lossy line parameters to match. An extra RC or two sometimes helps fine-tune the model to reality.
Multi-pair cables, like CAT5/6, can be expected to have various amounts of crosstalk and pair delay skews, too.
Simple RC equalization helps, if the cables are repeatable.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Thanks! Good collection of data there in your examples!
I do remember doing compensation BC (before CAD) using a pre-emphasis leading-edge pulse... on a thousand foot chunk ;-)
I'll look at how PSpice does their lossy T-line, and maybe I can adapt. I did some lecturing on skin-effect modeling for Intel eons ago... I'll review my notes. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
On Sun, 08 Dec 2013 11:55:30 -0700, Jim Thompson Gave us:
This has to be a first.
Or at least the first in a long time.
Could this mean that the group might actually get back on a/the scientific/proper track again?
Looks to me like you pointed him onto the right path, and also that he may actually know more about what effects are in play than you do, just has to dig up some recollection between glasses of wine or some such.
On Monday, 9 December 2013 07:20:30 UTC+11, DecadentLinuxUserNumeroUno wro te:
gs like compliant CAT5 and CAT6 cables.
gnores skin loss variation with frequency. The best thing to usually do is get a chunk of the actual cable of the expected length and note its step re sponse on a scope, then fiddle the Spice lossy line parameters to match. An extra RC or two sometimes helps fine-tune the model to reality.
of crosstalk and pair delay skews, too.
CAT6A_Tr.pdf
leading-edge pulse... on a thousand foot chunk ;-)
adapt. I did some lecturing on skin-effect modeling for Intel eons ago... I'll review my notes.
Scarcely. Larkin and Thompson have been posting here for a long time, and l iked each other a lot better early on.
Perhaps.
fic/proper track again?
It's never got off it. The political stuff is just background noise which s hows up when there's nothing technical to talk about.
-- Bill Sloman, Sydney
On Sun, 8 Dec 2013 16:54:07 -0800 (PST), Bill Sloman Gave us:
This from an asswipe who does not even know Usenet line length standards.
You cannot make a valid assessment when you are one of the main members of the class you claim to be describing.
I was around when the majority of posts were in abse.
And I am no idiot, Slotard. I *do* know how to use a 555 timer correctly. And I do understand its viability.
Probably here since late '94 or '95 on. You lose.
People in the know call that dispersion and it's way more complicated than looking at step response. It is also responsible for intersymbol interference and all that eye diagram slop.
On Monday, 9 December 2013 15:12:15 UTC+11, DecadentLinuxUserNumeroUno wro te:
meone who posts under a constantly changing alias is at a substantial disad vantage when he wants to claim to have been here for a long time. We did ha ve our resident idiots early on, but my feeling is that you weren't one of them.
s.
I know them, but Google doesn't respect them. I did have a Forte account fo r a while, but reading and posting via Google is easier.
of the class you claim to be describing.
In your opinion, which isn't worth much.
I wouldn't know about that. I've never been tempted to post to or read from the groups when posting binary files is acceptable.
correctly. And I do understand its viability.
Emphasising that you know how to use an obsolete device does suggest that y ou are intellectually challenged. The fact that it continues to be used in legacy circuits, and designed into new designs by legacy designers, isn't d ifficult to understand, and does explain why it continues to be a "viable" part. The people who keep on using it are another matter.
Anybody can make that kind of claim. Which pseudonym do you claim to have b een posting under at that time? It's easy enough to search the Google archi ves for that name, more difficult for you to prove that it's actually yours .
-- Bill Sloman, Sydney
"People in the know" don't call variation in skin loss "dispersion", they call it variation in skin loss. Dispersion happens even without skin loss.
In a linear system, which a cable is, the step response tells you everything there is to know about the system transfer function. It's the integral of the impulse response. If you know the step response, you can predict ISI for any data pattern.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Nah- dispersion generally means frequency dependent cable loss, sounds like skin effect among others, and this necessitates frequency dependent phase velocity, hence the intersymbol interference and smearing of non-sinusoidal waveforms.
That's the usual definition
yes, among others
Sure. And the step response describes it all.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
ut ignores skin loss variation with frequency.
than looking at step response. It is also responsible for intersymbol inte rference and all that eye diagram slop.
hey call it variation in skin loss. Dispersion happens even without skin lo ss.
ything there is to know about the system transfer function. It's the integr al of the impulse response. If you know the step response, you can predict ISI for any data pattern.
By definition, an integral lumps together the fine detail of the impulse re sponse - it's not going to tell you "everything", particularly when the edg e speed/transition time of the step to which your system is responding puts an upper limit on the frequency response bing probed.
Wrong. It means a frequency dependent difference in propagation velocity.
ersymbol interference and smearing of non-sinusoidal waveforms.
"Necessitates"? Dispersion is a frequency dependent difference in propagati on velocity, and necessarily smears out non-sinusoidal waveforms, where the various Fourier components are propagating at different velocities.
It convolves all the harmonics of the initial step. Deconvolving the compon ents can be tricky, and the harmonic content of a real - as opposed to a Di rac - spike only goes up to a limit defined by the width of the spike, or t he transition time of the step (which is the integral of a spike/impulse).
-- Bill Sloman, Sydney
On Sun, 8 Dec 2013 20:28:29 -0800 (PST), snipped-for-privacy@gmail.com Gave us:
He never did say he meant to transmit data packets.
fuzzy eye. Mr. Nyquist...
Inquiring minds want to know...
The book, , addressed SDL over standard ol' twisted telco lines. Is that of interest?
The results are a mix of formulas and empirical information supposedly better than 1% between DC and 10MHz for either 24 or 26 Awg twisted pair.
be careuful, my edition has 'errors' in them and you need to look at them before using them.
"ADSL/VDSL Principles" by Dennis J. Rauschmayer, 1999 Macmillan Technical Publishing pp 28-42
from URL:
ADSL/VDSL principles a practical and precise study of asymmetric digital subscriber lines and very high speed digital subscriber lines Dennis J. Rauschmayer. Published 1999 by Macmillan Technical Publishing in Indianapolis, IN . Written in English.
Aioe won't let me put in all the lines, so I'll send directly to you a sample of the 'corrected' formulas for 26Awg wire and uncorrected 24 Awg wire.
Anybody else want them, email me, or let me send to you and you can post them.
Got them, Robert, Thanks! ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
You're welcome. Were 'grunt' models what you were after? What you doing?
Yes, and you can't have frequency dependent propagation velocity without frequency dependent loss, and vice versa.
Actually, if you want to split hairs, and since you can't have a cable without a connector, connectorization does introduce nonlinear IP products if you look down far enough. HP Journal had an article on this effect, IIRC nickel was the bad actor.
does that include a lossless transmission line made up of Z(f) and C(f) elements?
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.