Twisted Pair
 

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 http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

Twisted Pair
 

On Sun, 08 Dec 2013 10:41:37 -0700, Jim Thompson
wrote:

Anyone have a decent Spice model for a twisted pair... lossy, not the
ideal model in circulation?

...Jim Thompson

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.

https://dl.dropboxusercontent.com/u/..._Risetimes.pdf

https://dl.dropboxusercontent.com/u/...tonewall_2.JPG

https://dl.dropboxusercontent.com/u/...P_CAT6A_Tr.pdf

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

Twisted Pair
 

On Sun, 08 Dec 2013 10:33:44 -0800, John Larkin
wrote:

On Sun, 08 Dec 2013 10:41:37 -0700, Jim Thompson
wrote:

Anyone have a decent Spice model for a twisted pair... lossy, not the
ideal model in circulation?

...Jim Thompson

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.

https://dl.dropboxusercontent.com/u/..._Risetimes.pdf

https://dl.dropboxusercontent.com/u/...tonewall_2.JPG

https://dl.dropboxusercontent.com/u/...P_CAT6A_Tr.pdf

Simple RC equalization helps, if the cables are repeatable.

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.