Extending Battery Life

By Ed Sperling
In the past it was all about clock frequency. People bought the latest computer and frequently paid a premium because it could crunch numbers faster. But as computing moves from the desktop into handheld devices, that focus is radically changing.

Low-Power Engineering caught up with Mark Bohr, senior fellow and director of Intel’s process architecture and integration, to talk about this shift and what needs to be solved in the future.

LPE: How much of a performance gain and an energy reduction do you get using Tri-Gate?
Bohr: In the low-voltage range, which is around 0.7 volts, we’re achieving about a 37% speed-up. Or conversely, another benchmark is power savings. If we benchmark these against our 32nm planar devices using Tri-Gate, we reduce active power by about 50%.

LPE: Is there any advantage in dropping the voltage lower than 0.7 volts?
Bohr: Yes, that is the name of the game now—to provide the lowest possible active power. Reducing operating voltage is a way of doing that. When I use 0.7 volts as the benchmark, that does not imply it’s the lowest voltage we can use.

LPE: What’s the foreseeable limit in terms of how low you can drop the operating voltage?
Bohr: That’s an important question for both process technology and circuit design. There’s no simple answer, but we are pushing that from both sides. On the transistor process side we are trying to make them usable from the lowest operating voltage. We also are bringing in some circuit design tricks to better enable low-voltage operation.

LPE: What are the challenges with that?
Bohr: There are two factors that you limit you as you try to drive operating voltage lower. One is for state retention on memory elements, like a static RAM cell. The other is performance and how controllable the performance is at a low voltage level. You have to fight both as you push voltage lower.

LPE: We’ve evolved into a society of impatient people, but is the concern now performance or plugging in your mobile device every night?
Bohr: My impression is that a lot of delays we see are not so much dependent on the speed of the processor but the bandwidth to memory.

LPE: We’ve been struggling with bottlenecks for decades, whether it’s I/O or memory. What’s changed?
Bohr: It’s not so much a microprocessor chip that operates at a higher frequency, but one that provides the performance level we expect on our desktop computers but in our hand. That’s where the power reduction is important.

LPE: It’s interesting how much power is now dominates Intel’s focus. What’s changed?
Bohr: It’s what the market wants. The market isn’t beating down our door for a 5GHz processor, even in a desktop solution. The fan noise is not going to be pleasant. People want high performance in their hand with long battery life.