[HN Gopher] Next-Gen Chips Will Be Powered from Below ___________________________________________________________________ Next-Gen Chips Will Be Powered from Below Author : jonbaer Score : 122 points Date : 2021-08-28 13:23 UTC (9 hours ago) (HTM) web link (spectrum.ieee.org) (TXT) w3m dump (spectrum.ieee.org) | ChrisMarshallNY wrote: | _> That 's up to three refrigerators, in your pocket!_ | | Bit misleading, there. A != W | marcosdumay wrote: | Current is the one number you look when talking about power | transmission. | ChrisMarshallNY wrote: | ...aother one, being Volts (which brings us back to...W). | Also AC/DC, Waveshape, RMS/Peak, Frequency, etc... | | W is watt _( "Watt" -geddit?)_ cooks your junk, if the phone | has a heat issue. | | Used to be an EE, back in the Dawn Times... | marcosdumay wrote: | Voltage is a completely different issue, that has only | indirect impact on "how big will this thing be?", at least | until you start measuring it by the hundreds. | | Of course, all of those are relevant, but the one number | that sizes the thing is current. | jagger27 wrote: | > it's consuming 200 W to provide its transistors with about 1 to | 2 volts, which means the chip is drawing 100 to 200 amperes of | current from the voltage regulators that supply it. Your typical | refrigerator draws only 6 A. High-end mobile phones can draw a | tenth as much power as data-center SoCs, but even so that's still | about 10-20 A of current. That's up to three refrigerators, in | your pocket! | | This feels out of place coming from IEEE. | nicoburns wrote: | Amps aren't really relevant here, I have a wrench that will | consume considerably more amps than that if you're able to | supply them. | marcosdumay wrote: | I don't see anything wrong with it. That refrigerator will be a | real constraint on the width of the power wires of any place | it's installed on. And adding the current of your devices is | exactly what you need to do to size your power lines. | | It being on IEEE, I can't imagine anybody on their target | audience will be confused and imagine they are talking about | power. | amelius wrote: | I don't know. I bet half of IEEE only worries about data/signal | processing in their dayjobs and never thinks about power | distribution. Such a comparison immediately makes clear what | the problem is. | [deleted] | maccolgan wrote: | >That's up to three refrigerators, in your pocket! This is the | part where it feels out of place | Keyframe wrote: | What is Ohm's law? Come on, IEEE! | rzwitserloot wrote: | Especially considering the fact that this is harping on about | Ampere. Which is _not_ the number to be looking at here; that'd | be watts. That fridge is chugging down 6A at 110 or 220V | (assuming it's a new fridge, unless its absolutely gigantic or | incredulously inefficient, sounds like that'd be a 110V model) | - not at 1 to 2 volts. | | If someone can build a fridge that is so efficient, it can make | do with 6A @ 2V, dang. Where can I buy me one of those? That's | 12W total, I can power one of these for a full hour with 4 AA | batteries. | wheels wrote: | I thought the same initially, and do think the analogy is | bad, but a few seconds later I wondered if the point that | they were making was that the interconnects carry the same | amperage: the required gauge for a connector (i.e. wire) is | determined by amps, not watts. As a result you can send more | power down smaller cables at higher voltages. | mindslight wrote: | That is the point they are making, but comparing it with | "three refrigerators" is seemingly invoking the power of a | fridge. | | To understand what they're saying, you need to understand | current as distinct from power regardless of the scale. If | you do understand this distinction, but you don't have a | feel for what 100 amps is, perhaps a good comparison is | starting a car. | [deleted] | willis936 wrote: | Yeah the ohmic losses in the power delivery networks are | the killer and the topic of this article. | throwaway9870 wrote: | As someone who has designed many chips, amperage absolutely | matters because it is not DC, it has very rapid transients | based on workloads and that, combined with inductance, can | make power delivery very difficult. Additionally, the high | current requires careful design of the package and routing | because of resistance and electromigration even in the DC | case. | Dylan16807 wrote: | > this is harping on about Ampere. Which is _not_ the number | to be looking at here; that'd be watts. | | You say that like it's obvious. I don't see why. | [deleted] | dghlsakjg wrote: | Amps is a measure of current. Then they switch to talking | about power which is measured in watts, but use amps as the | unit. Power measured in Watts is apples to apples. Amps are | only one half of the equation for watts. So comparing a | fridge to a phone is like.... comparing a fridge to a | phone. | | Watts are a function of Volts * Amps. So them talking about | a fridge using 6 amps at 120 volts is really quite a silly | comparison to using 200 amps at 1 volt. The fridge is using | 720 watts of power compared to 200 watts from the chip. | | In no way is it like having three fridges in your pocket. | Dylan16807 wrote: | They don't "switch to talking about power", they discuss | both the power and current to phone chips as opposed to | other chips. For fridges, they only mention amps. They're | not using the best wording but they're not doing what you | claim there. | lazide wrote: | It isn't, the example is confusing. It is about amps, as | this is due to very low voltage, very high amperage with | power movement. As the amperage is the interesting part | here (due to conductor sizing, losses to resistance, etc.) | dragontamer wrote: | Agreed. | | In my electrical engineering classes, we use amps to | determine the gauge of wires. | | The important calculation here is watts = I^2 * R | | Where R is the resistance of your wire, and watts is the | power wasted in your wires. | | And I is amps. That little squared sign is a bit | intimidating. Under normal circumstances, you want to | increase voltage to reduce wire loss. But computer chips | only operate at low voltage. | unnouinceput wrote: | And the reason they operate at low voltages has to do | with the micro-scale these SoC transistors are separated | from each other. Increase the voltage and you get a | shortcut, which will render your chip useless. | brennanpeterson wrote: | This is true but also wrong. The transistors themselves | have a specific operating voltage. | ASalazarMX wrote: | "[..] Austin Wilde held up the source of power that had | enabled a Disinto to chew up a mountain in half a second - | two flashlight batteries!" | | It's amazing how well Asimov's robot stories have aged in | these A.I. times. | bserge wrote: | A modern fridge compressor uses less than 300W (for a big | one). They're actually surprisingly efficient. | deepnotderp wrote: | Actually for power delivery networks current (amperes) is | mostly what you care about | whatshisface wrote: | Voltage drop = current x resistance. Power lost to heat = | current2 x resistance. I think they are making a reasonable | point that resistance losses are likely to be a much bigger | problem for a CPU than for a large appliance with similar | wattage. 10-20A is an enormous current even on household wires | (most household circuits are rated for 15-20A), and while wires | on CPUs are shorter, they're also a lot thinner. | | The wires in the refrigerator would likely be unable to handle | 20A at 2V. | bserge wrote: | No, they handle it fine. | konschubert wrote: | why? | | Amperage determines the wire diameter. High amperage means very | wide wires. | | I think their point is that this is what ultimately drives the | need to power from below. | ReactiveJelly wrote: | It's frustrating to see them not spare a couple sentences to | clear up a misconception that _many_ laypeople suffer from. | | Sure, _we_ know the difference between amps, watts, and watt- | hours, because we paid attention in science class, but most | people still get them mixed up. | wheels wrote: | To be fair, this is not a publication for lay-people; it's | obviously and explicitly a publication for electrical | engineers, which would not need these things explained. But | it's still a terrible analogy since the phrasing seems to | imply that it's talking about power, when it's actually | talking about current. | asddubs wrote: | because it would lead someone not already familiar with what | those figures mean and how they relate to one another to come | to the wrong conclusion. and someone who does know doesn't | need the analogy. When I think "fridge", I don't think "what | wire diameter do I need to deliver power", I think about a | big old hunk of metal using a bunch of power | JumpCrisscross wrote: | > _would lead someone not already familiar with what those | figures mean and how they relate to one another to come to | the wrong conclusion_ | | It's the IEEE. It's not designed for average consumption. | That's almost OP's point, which make this counterpoint a | bit comical. | asddubs wrote: | that's fair, although I would argue it's still a bad | metaphor, I had to do a double take to get what they were | getting at so it served to distract me rather than make | the point. | MayeulC wrote: | Instantaneous power draw can be quite considerable too, when | you have millions of transistors switching in a short lapse of | time. Typically you cannot really include capacitors on the | die, so those are close to it. It might have to do with it, but | I haven't read TFA yet. | bsder wrote: | Actually, inductive ringing on the power grid is generally a | bigger problem than lack of capacitance. | | Generally, not all the transistors in your chip switch. The | transistors that don't switch provide a charge reservoir to | draw from for the transistors that do. | | The problem is then backfilling all that current that got | lost and you have to do that _within one clock cycle_ --which | is the "lots of current" that this article is talking about. | | Because you have these pulses of current snapping from on to | off at fairly high frequencies being fed over long distances | with very little resistance to damp them, inductance kicks in | and starts causing oscillations (LC tank). | | However, at this point Moore's Law about performance is dead | (2x every 18 months), so this is not a very big deal. | | Moore's Law about cost is still alive (double the number of | transistors/halve the cost every 18 months). So, the big deal | currently is in the embedded space where leakage is more | problematic because the die is mostly determined by RAM and | flash sizes which goes directly to current leakage and die | size. | Zenst wrote: | Question I have is how much heat is generated by that power layer | and as it is copper, shifting that behind the silicon - would we | not see more thermal mass shifted to the backend of the CPU and | with a focus upon the top of the cpu for cooling solutions - how | would that pan out? Would we also need some heat-sink upon the | base of the CPU. Would we see extra heat shifted thru the silicon | layer with this process? | | One aspect that I've pondered that would save power would be | having the memory closer to the CPU and all that usable real- | estate for slots upon the reverse of the motherboard. Sure you | would be looking at new case designs in a way or existing ones | with new design considerations upon the mounting plate to have | gaps to accommodate sockets upon the reverse of the motherboard | PCB. That without having to compete with the CPU airspace for | cooling and in effect using the motherboard to zone things, could | work out well. | baybal2 wrote: | Most high end chips with high TDPs are already packaged upside | down. | | You CPU, or 9 out of 10 recent phone/tablet SoCs are all upside | down chips. | | https://en.m.wikipedia.org/wiki/Flip_chip | | So, it's actually going to be an improvement from the thermals | side, especially with TSVs carrying heat from the other side to | the heatsink. | ajaimk wrote: | Article says this: 10% loss budget in Front side power delivery | with a 7x improvement in the future => <2% of heat on bottom. | formerly_proven wrote: | Not really, no. Pretty much all LSI chips (and even a lot of | power / analog stuff these days) is flip chip, i.e. mounted | metal-layer down (if you see a BGA or waferscale package, all | of these are flip-chip). So the stackup looks like this | (roughly to scale): Heatspreader TIM | Silicon Silicon Silicon Silicon | Silicon Silicon Silicon Silicon | Silicon Active layer Metal layers Metal | layers Passivation Solder bumps and glue | Solder bumps and glue Solder bumps and glue | Solder bumps and glue Substrate/interposer/PCB | | What this article proposes is to put metal layers on BOTH sides | of the active layer, so you get more metal closer to it. That's | what they mean by "powered from below". If you look at a chip | today, they're all "powered from below" in the sense that the | metal layers are "below" the active layer and power (and all | signals) are fed in from "below" through the interposer. | Zenst wrote: | Thank you and appreciate the layer listing - most elegantly | done. | baybal2 wrote: | > they typically consume only about 200 to 400 watts per square | centimeter. | | That's quite a gross inaccuracy coming from the ARM researchers. | | Most chips barely get above 100W/cm2, and it's a very hard limit. | tus89 wrote: | I sure am sick of those ICs with pins sticking out of the top. | Progress at last! | nimish wrote: | This has already happened with cerebras and tesla dojo at least. | blendergeek wrote: | Source? I'd be interested in reading more about that. | nimish wrote: | https://fuse.wikichip.org/news/3010/a-look-at-cerebras- | wafer... | | Power fed vertically. Not sure it's BPR specifically, but | they do mention ~50% efficiency improvement in the PDN so | it's comparable. | rcMgD2BwE72F wrote: | https://www.youtube.com/watch?v=QurtwJdb5Ew&t=229 | hliyan wrote: | The metal-filled trenches in the silicon need to survive high | temperatures, so according to the article copper is out of the | question. They "experimented with ruthenium and tungsten" but | it's not clear whether they actually built something or whether | it was all simulation. Either way, this is likely to make the | chips more expensive. | unnouinceput wrote: | It's a simulation, they don't even have a prototype yet. Quote: | "Simulation studies are a great start, and they show the CPU- | design-level potential of back-side PDNs with BPR. But there is | a long road ahead to bring these technologies to high-volume | manufacturing. There are still significant materials and | manufacturing challenges that need to be solved. " | brennanpeterson wrote: | I doubt this is true. Mike Mayberry (Intel) softly announced | buried power rail last year, as a 'within 5 years' tech. That | suggests it has been prototyped, since from final tests to | HVM is at least 2 years. | | Maybe not great. | | Within 10 means an idea with simulation. Within 5 means | prototyped. Interesting means never. Or that, at least, is my | decoder ring. ___________________________________________________________________ (page generated 2021-08-28 23:00 UTC)