6 Feb
2012
6 Feb
'12
5:38 a.m.
On 5 Feb 2012, at 9:01 PM, Mouse wrote:
[snip]
I'm still mystified. How do people treat
ground-and-negative power
differently from ground-and-positive that makes ground stabler?
IIRC, there's a couple of things at play here:
- Ground is presumed to be the most stable voltage in the system (I believe this is *the*
reason that ECL is *specified* as positive ground) by virtue of the fact that it's
usually nothing more than a (distributed) hunk of metal with only parasitic devices
associated with it.
- ECL is more or less immune to noise on Vee but fairly sensitive to it on Vcc.
That's not to say that you can't build ECL that works as you suggest; there's
+5 PECL out there as well as +3.3V LVPECL; I believe that both are differential systems.
--
Dr. Christian Kennedy
chris at mainecoon.com AF6AP
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