[HN Gopher] Interesting BiCMOS circuits in the Pentium, reverse-...
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Interesting BiCMOS circuits in the Pentium, reverse-engineered
Author : DamonHD
Score : 29 points
Date : 2025-01-21 17:23 UTC (5 hours ago)
(HTM) web link (www.righto.com)
(TXT) w3m dump (www.righto.com)
| kens wrote:
| Is BiCMOS radical woke? :-) Author here for your Premium
| questions...
| smegsicle wrote:
| whats that supposed to be some kind of sick joke?
| kens wrote:
| No. I'm making fun of the comments on my previous article
| that called me "radical woke."
| java-man wrote:
| Oh please, we are all a bit sensitive right now.
|
| We always enjoy reading your articles, Ken!
| hulitu wrote:
| BiCMOS was supposed to be faster than CMOS. Whas this the case
| with this processor ?
| kens wrote:
| Intel said that BiCMOS decreased signal delays by up to 35%,
| although the total performance improvement would be less.
| chasil wrote:
| What areas still use bipolar? Does a switching power supply use
| substantial bipolar? Does anybody still implement TTL or ECL?
|
| Quoting you below...
|
| "The most unusual circuit is the BiCMOS driver. By adding a few
| extra processing steps to the regular CMOS manufacturing
| process, bipolar (NPN and PNP) transistors can be created. The
| Pentium extensively used BiCMOS circuits since they reduced
| signal delays by up to 35%. Intel also used BiCMOS for the
| Pentium Pro, Pentium II, Pentium III, and Xeon processors.
| However, as chip voltages dropped, the benefit from bipolar
| transistors dropped too and BiCMOS was eventually abandoned."
|
| I didn't realize that BiCMOS lasted so long. I thought it was
| only used on the original Pentium, but I really didn't look
| hard.
|
| Edit: BiCMOS has a wiki.
|
| https://en.wikipedia.org/wiki/BiCMOS
| RicoElectrico wrote:
| I think the best keyword to seek is BCD (Bipolar, CMOS, DMOS)
| which is a process pioneered by ST. It is quite alive indeed.
|
| Bipolar has for example lower noise than CMOS when it comes
| to opamps.
| qwezxcrty wrote:
| Lower noise for lower source impedances, to be slightly
| more precise.
| rossdavidh wrote:
| Ah, memories. I was a manufacturing engineer in a bipolar factory
| from 1989 to 1992, and BiCMOS was the perennial hope for a future
| for our acquired skills. When word broke that the Pentium would
| have one, it seemed significant. On the whole, though, it didn't
| have the impact that was hoped for; bipolar hangs on (like COBOL)
| in certain niches, but I think despite the theoretical
| advantages, the disadvantages of having to think about both
| bipolar and CMOS transistors in the engineering, was too much of
| a price to pay.
|
| Lesser known reasons: as bipolar transistors went to polysilicon
| gates (which have a tiny, ~1-2 Angstrom thick layer of oxide in
| them) and MOS transistors started to become leakier through their
| ever-shrinking gate oxides, the distinction between MOS and
| bipolar transistors became fuzzier. Modern MOS transistors leak
| less current through their gate oxides than the bipolar
| transistors did through the polysilicon emitter, but the physics
| of the two is not as different as it was twenty years ago.
| FuriouslyAdrift wrote:
| I remember the Exponential Technologies bipolar PowerPC chip
| running at 533 MHz back in 1997... so sad Apple killed it
|
| https://web.archive.org/web/19970712065424/http://www.byte.c...
| kens wrote:
| That's an interesting chip. You don't see many bipolar
| processors. (The Pentium has a few bipolar transistors
| sprinkled around, but it's mostly CMOS.)
| formerly_proven wrote:
| DEC made a one-off ECL CPU in 1993:
| https://bitsavers.org/pdf/dec/tech_reports/WRL-93-8.pdf
|
| 300 MHz / 115 W. Ten years later, you'd have Pentium 4 at
| 3000 MHz and 115 W.
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