19 Feb
2022
19 Feb
'22
11:15 a.m.
On Feb 19, 2022, at 1:28 PM, Jon Elson via cctalk
<cctalk at classiccmp.org> wrote:
On 2/18/22 21:43, ben via cctalk wrote:
I think there are a number of reasons why ECL was niche technology. One is that TTL was
fast enough for most applications. Another is that more people knew TTL, and ECL requires
(some) different design techniques. Yet another is that higher levels of integration
appeared in CMOS but not ECL. Yet another is that ECL was expensive compared to the
alternatives, partly because of the low integration and partly because of the low volume.
In the mid-1980s (I think) there was a very interesting project at DEC Western Research
Lab to build a custom VSLI ECL processor chip. A lot of amazing design was done for it.
One is power and cooling work; it was estimated to consume about 100 watts which in that
day was utterly unheard of, by a substantial margin. This was solved by a package with
integral heat pipe. Another issue was the fact that ECL foundries each had their own
design rules, and they were shutting down frequently. So the CAD system needed to be able
to let you specify a design where the fab rules were inputs to the layout algorithms. The
design took great advantage of ECL-specific logic capabilities like wire OR or stacked
pass transistors. I remember that the CAD system let the designer work at multiple levels
in the same chip: at the rectangle level (for memory arrays), transistor level, gate
level, and even write some constructs as programming language notations. For example a
64-bit register could be specified as:
for (i = 0; i < 64; i++) { transistor-level schematic of a one-bit register }
Originally the idea was to use this for a 1 GHz Alpha; I think it ended up being a 1 GHz
MIPS processor. Possibly the project was killed before it quite finished.
That seems to have been one of the very few examples of ECL going beyond SSI. The
physical possibility existed; the economics did not.
paul
The 70's was all low scale tech. I suspect it was the high speed/edge rates more the
power that kept ECL from common use. Any other views on this topic. Ben, who only had
access to RADIO SHACK in the 70's.
PS: Still grumbling about buying life time tubes at a big price,
just to see all tubes discontinued a year or two later.
Edge rates on pedestrian MECL 10K were not crazy fast. Rise and fall of about 1 ns, but
the gate propagation delay was ALSO about 1 ns, so that was a lot faster than TTL. ECL
was very easy to work with, crosstalk was not a common issue. But, you HAD to terminate
any line over a foot, and better to make it 6" to be sure. And, the termination and
pulldown resistors ate a LOT of power!