ECL: Why'd they use negative voltages?
in [Design]
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From: John Larkin on 7 Jun 2010 20:41 On Mon, 07 Jun 2010 19:27:41 -0500, "krw(a)att.bizzzzzzzzzzzz" <krw(a)att.bizzzzzzzzzzzz> wrote: >On Mon, 7 Jun 2010 16:56:24 -0700, "Joel Koltner" ><zapwireDASHgroups(a)yahoo.com> wrote: > >>I realize it was the early '60s and all, but why does ECL generally use 0V for >>VCC and -5.2V for VEE, rather than, oh, say... 5V for VCC and 0V for VEE? >>Something related to how things were done when toobs ruled? (I realize that >>you can almost always run ECL off of 5V/0V -- and apparently this was popular >>practice at one time?) > >Add to the above, shorting the common emitter outputs to ground isn't >damaging. > >>And why 5.2V anyway? (Granted, 5.2V is no stranger than 6.3V filament >>transformers, I suppose...) > >Stack up the voltages (don't forget the AND gate). > >Not all ECL was the same, though. Our high performance ECL ran off +1.25V and >-3V, with the outputs around ground. +2 and -3 allow terminations to ground. Terms are where most of the power goes. John
From: krw on 7 Jun 2010 20:43 On Mon, 7 Jun 2010 17:35:05 -0700, "Joel Koltner" <zapwireDASHgroups(a)yahoo.com> wrote: ><krw(a)att.bizzzzzzzzzzzz> wrote in message >news:4e3r065vr383q2hc9fiuhre2mu9opopbai(a)4ax.com... >>>And why 5.2V anyway? (Granted, 5.2V is no stranger than 6.3V filament >>>transformers, I suppose...) >> >> Stack up the voltages (don't forget the AND gate). > >Purportedly it'll run down to around VCC-VEE = 3V and up to about 8V before >you start seeing massive performance differences. 5.2V is certainly pretty >close to the center of those two... hmm... I wouldn't be surprised if that's >how they came upon it! No, Jim had the reason above. Try an AND gate at 3V. ;-)
From: Joel Koltner on 7 Jun 2010 20:44 Thanks John, that's quite informative. "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:di3r0613v9lkk2p8dq06snde2hgopt87fr(a)4ax.com... > Newer stuff, like EclipsLite, works at 3.3 volts, and some at 2.5. I > do mixed-mode PECL and cmos/FPGAs off a +3.3 volt supply. That's kinda what prompted the question -- Joerg has been pointing me at some of the high-speed logic from the likes of Micrel, and I was reading up some in the old MECL System Design Handbook so that I hopefully won't embarrass myself too badly when I go to use some of it. :-) ---Joel
From: D Yuniskis on 7 Jun 2010 20:47 Hi Joel, Joel Koltner wrote: > I realize it was the early '60s and all, but why does ECL generally use > 0V for VCC and -5.2V for VEE, rather than, oh, say... 5V for VCC and 0V You also had a Vbb of around -1.2V (?). Lines were typically terminated to this. > for VEE? Something related to how things were done when toobs ruled? (I > realize that you can almost always run ECL off of 5V/0V -- and > apparently this was popular practice at one time?) > > And why 5.2V anyway? (Granted, 5.2V is no stranger than 6.3V filament > transformers, I suppose...) Dunno. But, it was fast and ate gobs of power. In the mid 70's I worked on a processor (i.e., what nowadays would be a CPU "chip") that drew 100A (MECL III and 10K). "Bus bars" for power were 3/4" square copper shafts. Instruction cycle time was 8ns. By comparison, I think a 7404 (inverter) takes *7* ns just to change the state of its output. If you "slipped" when pulling/installing a chip, the legs would vaporize before the power supply would even hiccup. (needless to say, you removed all jewelry -- belt buckles, eye glasses, rings, etc. -- when working on it)
From: Joel Koltner on 7 Jun 2010 20:46
"Joerg" <invalid(a)invalid.invalid> wrote in message news:875hpjFk48U2(a)mid.individual.net... > And cars had DC generators. In fact, my old Citroen did as well. > Crankshaft-driven, no belts in the whole car. Seems like a belt is an awfully inexpensive addition for the flexibility it provide in terms of being able to locate and size your generator independently of the engine itself, to a large extent! |