[SI-LIST] Re: impedance determination of a perticular interface.....
- From: <colin_warwick@xxxxxxxxxxxx>
- To: <malli.1729@xxxxxxxxx>
- Date: Sun, 21 Sep 2014 14:12:22 +0000
Hi Mallikarjun,
Steve Weir pointed out to me off list that I might have misunderstood your
question "What drives these characteristic impedance values? "
At first blush I thought you meant "What physical quantities drive
characteristic impedance values?" but on mature reflection you may have meant
"What design goals drive us to seek a particular impedance target?"
It turns out that there's a lot of fuzzy urban myth about how the 50 ohms (or
75 ohms or 300 ohms) standards came about. There's a good essay with some
plausible arguments here:
http://www.microwaves101.com/encyclopedias/458-why-fifty-ohms
According to the essay, the historical design goals that led to the 50/75/300
ohm standards aren't relevant to SI because (for example) we don't use co-ax
t-lines much (especially air-spaced co-ax t-lines) and maximal power handling
isn't generally a goal in SI. However 50 ohms lives on through "installed
base" inertia. Let's say connector manufacturers have historically made 50 ohm
connectors. Then, all else equal, you might design everything else to match
that just to leverage the high volume/low cost connector.
Best regards,
-- Colin
____________________
Colin Warwick
Product Manager for Signal Integrity, Power Integrity, and EMI/EMC tools for
High-Speed Digital Design
Keysight EEsof EDA
Phone +1 978 681 2406
colin_warwick@xxxxxxxxxxxx
Blog updates: http://signal-integrity.blogs.keysight.com/newsletter/
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
