SAN JOSE, Calif. Intel Corp. is dropping its power budget guideline for notebook computers from the current 12.6-watt level to just under 10 watts for 2003, said Don Nguyen, senior power architect at Intel.
Speaking Thursday (Feb. 20) at the Intel Developer Forum here, Nguyen said the savings are to come from a rethinking of how power is distributed and consumed in the notebook platform. He took aim at the biggest target, the backlit display, which consumes one-third of total platform power. Long-term, some savings will come from the move to low-temperature polysilicon display technology, where the larger aperture ratio results in a need for less backlight.
But in the meantime, a substantial savings in power could be had by much simpler means. In current designs the platform power supply converts battery voltage down from around 9 V to 3.3 V for distribution. The display module promptly steps this voltage back up to a higher voltage to drive the display, incurring an overall conversion loss of about 25 percent. By simply taking the higher voltage directly from the battery or AC adapter, nearly a quarter of the display power could be saved, he said.
Further savings could be had by installing an intelligent ambient light sensor that reduces backlight power in response to reduced ambient light, and by improving the backlight regulator efficiency at low loads.
Also, the Windows XP operating system continuously polls the DVD controller in support of its auto-play feature. This not only requires keeping the controller awake a 300 mW cost all by itself but it prevents Intel's latest CPUs from entering their best low-power modes.
Nguyen said that all of the dc-dc converters in the notebook platform suffer from decreased efficiency because they must accept an input voltage that ranges from the low end of the battery voltage: around 9 V, up to the ac adapter output, which for legacy reasons remains around 20 V. By slight design changes to the charger circuit and battery packs, the charging circuit could double as a down-converter for the ac supply, keeping the platform power bus in the 9-12 V range and permitting the design of significantly more efficient converters for the CPU, display and other components, he said.
Finally, Nguyen said that many of these savings have secondary effects. Supplying higher voltage to the display panel reduces the current -- and the resistive loss -- in the flexible cable between the main power supply and the panel. Improving regulator efficiency reduces the enclosure temperature, since the regulator heat is dissipated directly into the enclosure, not into the CPU heat removal system. That reduces the ambient temperature for the CPU chip, which in turn reduces leakage current, and hence power dissipation, in the CPU.