Intel is slowly but surely moving more platform components onto the processor. Over the years, the graphics, PCI Express, and memory controllers traditionally found on separate north-bridge chips have migrated onto the CPU die. With Haswell, voltage regulation is also coming onboard. EXPreview has posted leaked slides that detail the voltage regulator inside Intel’s next-generation CPU.
The FIVR, or Fully Integrated Voltage Regulator, promises higher efficiency, finer granularity, and cleaner power delivery than traditional solutions, which rely on the motherboard for voltage regulation. The FIVR apparently consolidates CPU core, graphics, system agent, I/O, and PLL voltage regulation into a single unit. Voltage regulation for the memory is still handled separately by the motherboard, though.
According to the slides, the FIVR is based on a multi-cell architecture with 20 cells per chip. Each cell behaves like a mini regulator and is capable of handling current up to 25A. The switching frequency of the cells is programmable between 30 and 140MHz, the slides say, and there are 16 power phases per cell. You’re looking at 320 phases per chip, which is quite a lot.
The slides credit the large number of power phases with reducing ripple and noise. Voltage ripple is "almost non-existent," with worst-case scenarios yielding no more than +/- 0.002V. The voltage drift due to temperature increases is apparently just 0.001V. Those figures appear to refer to a 90-nm version of the power cell. Haswell’s implementation should be built with more advanced 22-nm transistor tech.
Even when fabbed with 90-nm tech, the integrated regulator is said to be about 50 times smaller than typical motherboard implementations. There is a cost, though. Because the regulator is part of the CPU, it contributes to the thermal footprint of the chip. Perhaps that’s why the TDP of high-end Haswell processors is 84W, up from 77W for Ivy Bridge.
Haswell’s FIVR was surely designed with mobile in mind, and it will no doubt pay dividends in highly integrated systems like tablets and notebooks. Desktop users can probably look forward to greater power efficiency, too. That said, overclockers may hit thermal limits sooner than they did with Ivy-based chips, and motherboard makers will need to find new ways to hype their boards’ power regulation circuitry.