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100-GHz Single-Flux-Quantum Bit-Serial Adder Based on 10-KA/Cm2 Niobium Process
- peter_d_sherman 6y agoRelated: "Automatic Single-Flux-Quantum (SFQ) Logic Synthesis Method for Top-Down Circuit Design" https://iopscience.iop.org/article/10.1088/1742-6596/43/1/287/pdf https://iopscience.iop.org/article/10.1088/1742-6596/43/1/28... >"Abstract. Single-flux-quantum (SFQ) logic circuits provide faster operations with lower power consumption, using Josephson junctions as the switching devices. In the top-down flow of SFQ circuit design, we have already developed a place-and-route tool that covers backend circuit design. In this paper, we present an automatic SFQ logic synthesis method that covers front-end circuit design. The logic synthesis is a process that generates a gate-level logic circuit from a functional specification written in hardware description languages. In our SFQ synthesis method, after we generate an intermediate circuit with the help of a synthesis tool for semiconductor circuits, we convert it into a gate-level pipelined SFQ circuit. To do this, an automatic synthesis tool was implemented." PDS: Phrased another way, the idea here can basically be boiled down to: For the most time-critical parts of a conventional CPU, i.e., the Adder/ALU -- instead of using conventional circuitry for that, let's use circuits specifically designed for Quantum Computers because of their fast switching speed... The end result is that you still get a conventional digital CPU -- albeit, in theory, a much, much faster one... The "magic phrase" (for research) for all of this -- is Single-flux-quantum (SFQ) logic circuits...
- marcodiego 6y agoWhen I read about quantum computing the impression I get is that quantum computers are more similar to analog computers than to classical computers. That is, there are a problems where they are better/faster than classical computer and problems where classical are better/faster than quantum computers. Having a "100-GHz Single-Flux-Quantum Bit-Serial Adder" means we can finally have hope for classical computations at hundreds of GigaHertz?
- packetlost 6y ago> quantum computers are more similar to analog computers I can't speak for all architectures, but the ones I'm aware of absolutely are analog computers.
- Robotbeat 6y agoQuantum computers use qubits, which doesn’t really have an analogue in analog computers.
- packetlost 6y agoNot directly, but the problems and engineering that go into building one are very similar. Qubits are analogous to regular bits, at least on 'measure'. They're either in 1 state or another, and all the interesting stuff is in how you get to that state. Source: building a quantum computer.
- Robotbeat 6y agoYes, that’s my point! The person I’m responding to is saying they’re like analog computers, which don’t use bits. Quantum computers are a bit more like digital computers.
- packetlost 6y agoI am the person who said that :) I guess what I really meant was I agree with your original statement. They're closer to analog computers than digital, but really they're neither and share some similarities of both. In the sense that the qubits usually only have 2 measurable states in computation, they're similar to digital computers, but that only goes for when you measure. On the other side, the 'programs' going in are not really digital information (though they can be represented as such), and because qubits are not only in one of 2 states (unlike bits) the way in which you interact/program them is definitely not digital, it is analog. If you're interested in learning about writing quantum programs, I recommend checking out IBM's Qiskit toolkit[0]. I found the tutorials to be helpful for helping grasp the fundamentals of quantum programming. [0]: https://qiskit.org/documentation/getting_started.html https://qiskit.org/documentation/getting_started.html
- thatcherc 6y agoTo be clear, despite the appearance of 'quantum' in the title, this is a development toward faster classical computers by using superconducting circuit elements (Josephson junctions). A computer using this type of logic would need to be cryo-cooled down to ~single-digit Kelvin temperatures, but as discussed in a thread a few weeks ago[0], a superconducting computer can still beat a conventional computer in terms of ops/Watt, even when the power consumption of the cooling equipment is included. [0] - https://news.ycombinator.com/item?id=25765128 https://news.ycombinator.com/item?id=25765128
- HPsquared 6y agoVery cool!
- wiz21c 6y agoCool as cold ?
- deleted 6y ago[deleted]
- mdip 6y agoThanks for summing that up; based on the title, alone, I was considering clicking because I so rarely encounter a sentence such as this: containing so many words I know/use regularly yet when put together in that precise manner, appeared to be as to have been assembled by a garbage disposal.
- contravariant 6y agoTheoretically keeping something at the same temperature is at most going to double the energy requirements, though there's likely to be some additional practical issues with maintaining such a low temperature.
- amluto 6y agoNot even close. A perfect refrigerator will use vastly more than 1J to remove 1J from a 4.2K device. Look up Carnot’s theorem.
- jjoonathan 6y ago170 GHz is the speed of a PLL published by a popular chip designer on youtube a decade ago in 130nM SiGe BiCMOS. The "100GHz" headline tempts comparison to CPU clock speeds but those are absolutely not the right point of comparison. GHz doing one thing != GHz doing another. CPU clock cycles are very deep compared to a bit-serial adders and operate under heavy thermal constraints. To compare apples to apples, we need to know: what is the speed of a bit-serial adder in near-future CMOS? Silicon bipolar? 3-5 bipolar? My guess: you could implement a 100GHz bit serial adder in CMOS today and get several hundred GHz if you dropped thermal constraints, went bipolar, etc. That doesn't invalidate the research -- we need more public cutting-edge device research, not less -- but the posts assuming this result translates to 100GHz CPUs are getting a bit ahead of themselves.
- mlyle 6y agoAs you say-- it depends upon what you're doing. Comparing a PLL to an adder is silly. > My guess: you could implement a 100GHz bit serial adder in CMOS today 7nm FINFET CMOS will get you to roughly the same performance point. It's also quite mature compared to the technique in the article.
- jjoonathan 6y ago> Comparing a PLL to an adder is silly. Yeah, but comparing a bit adder to a 64 bit full adder integrated into a modern CPU clock cycle is really silly :) Glad to hear my intuition about modern CMOS was in the ballpark though. I've been out of this scene for the better part of a decade.
- mlyle 6y agoRing oscillators and bit adders and 30 gate benchmark circuits are how we characterize processes. We don't try and fabricate a superscalar CPU on our first round trips through developing a new process let alone new transistor types. This is doing quite well for early rounds on this technique.
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- hdjfjrbrbt 6y agoAt 100 GHz signals can only propagate 3 cm per clock. So to run at those speeds, you need extremely compact circuits, and you need to bring memory closer too. Maybe move to 3D, another way to increase reach. What is the current thinking regarding this problem?
- ben_w 6y ago3mm rather than 3cm, but also note that full CPUs have to run slower than the upper limit of the transistors inside them, because most operations need to go through multiple transistors.
- jjoonathan 6y agoCaches are already closer than 3cm and can take multiple cycles to fetch from. DRAM takes 100s of clock cycles to fetch from! It's bad -- but the badness was already here. Propagation delay problems are real, but for caches IIRC the biggest problems are transmission lines being lossy and having propagation speeds much slower than the speed of light in a vacuum, and for DRAM the biggest problems are waiting for precharge and waiting for the sense amplifiers to stabilize. Waiting for the precision required to read obscenely small capacitors, in other words. If DRAM is 1T1C and SRAM is 6T, I always wondered why we couldn't just have DIMMs of SRAM at 1/3rd the capacity or whatever. Overprovisioning DRAM by that factor is already common, wouldn't eliminating all the downtime be a way to put that slack to work? Like the HDD -> SSD transition? Ah well, I'm sure there's a constraint I'm just not thinking of.
- simcop2387 6y agoYou'd need a different CPU these days since the memory controller for sram would be a bit different. That said you do see sram in smaller embedded systems because it's also easier to drive and work with signal wise. I bet someone's done it as a research project with larger CPUs but I bet the cost of the SRAM and the cost of a niche cpu design just made it all not viable in the market place.
- jjoonathan 6y ago
- ajb 6y agoThere have been attempts to make these SFQ circuits work for ages, eg see this from 1999: https://www.researchgate.net/publication/3310945_Rapid_Single_Flux_Quantum_T-flip_flop_operating_up_to_770_GHz https://www.researchgate.net/publication/3310945_Rapid_Singl... What I want to know is, what were the problems that prevented them succeeding before, and have they been overcome now?
- ThePhysicist 6y agoI designed such superconducting chips for my MSc thesis and had them manufactured by Hypres, one of the few foundries that offered such a process. Designing superconducting circuits is great fun, I even wrote my own circuit simulator (https://github.com/adewes/superconductor/ https://github.com/adewes/superconductor/). RSFQ (Rapid Single Flux Quantum Logic, or as some would jokingly say Russian Single Flux Quantum Logic) was quite hyped up in the nineties, Prof. Likharev at Stony Brook had a collaboration with IBM working on RSFQ circuit elements to replace conventional semiconductor logic. At the time the achievable speed was fantastic as compared to regular circuits, (un)fortunately semiconductor processes kept evolving and today RSFQ is only interesting for some niche applications like fast microwave circuits at cryogenic temperatures (and even there HEMT transistors are often a better solution nowadays). Also, getting circuits with more than 10.000 junctions to work was quite tricky as the fabrication processes weren't very reliable and transferring flux quanta is a bit more noisy than storing charges on an FET, so I'm doubtful whether we could even have large-scale RSFQ circuits without extensive error correction. Well, it's still an amazingly fun and fascinating field, really hope we might see a revival of it one day (maybe if we get room-temperature superconductors).
- ByThyGrace 6y ago> (maybe if we get room-temperature superconductors). Since you sound like the appropriate person to ask, what is the current state of research towards room-temperature superconductors?
- ThePhysicist 6y agoI'm not up-to-date on that research area but there's a lot of research going on (see [1] for an overview) and people are both trying new material combinations and trying to figure out what exactly causes superconductivity (which still isn't fully understood for high-Tc superconductors). BTW it would already open up many new opportunities if we had a superconductor that could be patterned as easily as a regular semiconductor and that would work at "high" cryogenic temperatures (e.g. -40 or - 80 °C), as those temperatures can be easily attained with conventional coolers that don't rely on liquid nitrogen or (much more expensive) liquid hydrogen or (super expensive) a mixture of different Helium isotopes. So far there's no fundamental reason that superconductivity can't work at higher temperatures, but there's also no clear path to room-temperature superconductors as far as I'm aware. [1]: https://phys.org/tags/high+temperature+superconductors/ https://phys.org/tags/high+temperature+superconductors/
- AI_WAIFU 6y agoThis paper is over 10 years old.
- baxtr 6y agoIs this a real title or was this title generated by GPT-3?