3 ms·

Am I mistaken that those 200 amps are distributed among billions of transistors? Is there any point where there is a single conductor carrying 200A? I would ha

Am I mistaken that those 200 amps are distributed among billions of transistors? Is there any point where there is a single conductor carrying 200A? I would have thought that the actual power distribution is done some other way. How does this 200A actually work in practice? Do they start with higher voltage and step down? This poor analogy means I don’t understand the problem that’s been solved. I would really have liked to learn this from the article, but instead all I can think of is the one noisy compressor in my 20yo fridge sucking down 6A (probably 3A where I live) over cables almost as thick as a CPU is wide.

magicalhippo 5y ago
Yes, the 200 amps are consumed by the billions of transistors. As you might have noticed, these power-hungry chips have a large number of pins, and quite a lot of them are dedicated to power, exactly to avoid having a single pin having to carry 200 amps. Here's[1] the pinout of the AM4 socket, where the pink and green squares represents power and ground respectively. As you can see they make up almost half of the pins. The motherboard is primarily supplied by 12V these days, which is then converted down to the 1-2V needed using multi-phase buck converters[2]. If you've ever seen motherboards boasting some number of VRM phases, this is what they're talking about. Gamers Nexus has an overview[3] of this as well. The problem they're talking about is similar to the AM4 socket. You have a bunch of signal pins, and they're connected to output transistors inside the package. You'd like to avoid long connections, so ideally the pin is close to the relevant output transistors on the chip. However you also got all this power that needs to be supplied, and you gotta spread that out over multiple pins. So it's a challenge to best arrange the power vs signal pins, minimizing the detours either have to take. Long connections means higher inductance and resistance, which is a problem for both signal and power. Imagine instead the CPU was mounted like a sandwich, with pins on both sides. Then it would be easy, as you could just place all the power pins on one side and signal pins on the other side. This is the solution they propose, except on the chip level. [1]: https://www.docdroid.net/6cDW11N/am4-pinout-diagram-pdf https://www.docdroid.net/6cDW11N/am4-pinout-diagram-pdf [2]: https://en.wikipedia.org/wiki/Buck_converter#Multiphase_buck https://en.wikipedia.org/wiki/Buck_converter#Multiphase_buck [3]: https://www.gamersnexus.net/guides/1229-anatomy-of-a-motherboard-what-is-a-vrm-mosfet?showall=1 https://www.gamersnexus.net/guides/1229-anatomy-of-a-motherb...
- doctor_eval 5y ago
  Thanks for your reply. That makes sense. So would I be right to say that the problem is that the way power is delivered to individual transistors is getting too complex while the features are getting too small? The article started out by focussing on the total current at transistor voltages, but at 12 volts to the chip it’s just ~16 amps (still a lot!), spread across say 100 pins = 160mA per pin. Which isn’t as impressive as 200A. 200A is clearly not a wire you see going into a CPU. It’s a shame that the article seems to have chosen to oversimplify the problem at the expense of helping us understand. The complexity of power delivery from the top of the chip looks fascinating, but it lost me at the outset with claims that wouldn’t pass muster with a high school electronics enthusiast.
  - magicalhippo 5y ago
    > but at 12 volts to the chip It's the chip itself that needs 1-2V, so the buck converter is on the motherboard. So indeed 200A enters the chip. The linked GN article has a nice overview of the motherboard VRM layout. The AM4 socket has 1331 pins though, so with roughly a quarter of those sourcing current that's 0.6A per pin (the other half of the power pins sinks that current).

magicalhippo 5y ago

Yes, the 200 amps are consumed by the billions of transistors. As you might have noticed, these power-hungry chips have a large number of pins, and quite a lot of them are dedicated to power, exactly to avoid having a single pin having to carry 200 amps. Here's[1] the pinout of the AM4 socket, where the pink and green squares represents power and ground respectively. As you can see they make up almost half of the pins. The motherboard is primarily supplied by 12V these days, which is then converted down to the 1-2V needed using multi-phase buck converters[2]. If you've ever seen motherboards boasting some number of VRM phases, this is what they're talking about. Gamers Nexus has an overview[3] of this as well. The problem they're talking about is similar to the AM4 socket. You have a bunch of signal pins, and they're connected to output transistors inside the package. You'd like to avoid long connections, so ideally the pin is close to the relevant output transistors on the chip. However you also got all this power that needs to be supplied, and you gotta spread that out over multiple pins. So it's a challenge to best arrange the power vs signal pins, minimizing the detours either have to take. Long connections means higher inductance and resistance, which is a problem for both signal and power. Imagine instead the CPU was mounted like a sandwich, with pins on both sides. Then it would be easy, as you could just place all the power pins on one side and signal pins on the other side. This is the solution they propose, except on the chip level. [1]: https://www.docdroid.net/6cDW11N/am4-pinout-diagram-pdf https://www.docdroid.net/6cDW11N/am4-pinout-diagram-pdf [2]: https://en.wikipedia.org/wiki/Buck_converter#Multiphase_buck https://en.wikipedia.org/wiki/Buck_converter#Multiphase_buck [3]: https://www.gamersnexus.net/guides/1229-anatomy-of-a-motherboard-what-is-a-vrm-mosfet?showall=1 https://www.gamersnexus.net/guides/1229-anatomy-of-a-motherb...

doctor_eval 5y ago
Thanks for your reply. That makes sense. So would I be right to say that the problem is that the way power is delivered to individual transistors is getting too complex while the features are getting too small? The article started out by focussing on the total current at transistor voltages, but at 12 volts to the chip it’s just ~16 amps (still a lot!), spread across say 100 pins = 160mA per pin. Which isn’t as impressive as 200A. 200A is clearly not a wire you see going into a CPU. It’s a shame that the article seems to have chosen to oversimplify the problem at the expense of helping us understand. The complexity of power delivery from the top of the chip looks fascinating, but it lost me at the outset with claims that wouldn’t pass muster with a high school electronics enthusiast.
- magicalhippo 5y ago
  > but at 12 volts to the chip It's the chip itself that needs 1-2V, so the buck converter is on the motherboard. So indeed 200A enters the chip. The linked GN article has a nice overview of the motherboard VRM layout. The AM4 socket has 1331 pins though, so with roughly a quarter of those sourcing current that's 0.6A per pin (the other half of the power pins sinks that current).