Powering cellular base stations around the world will cost $36 billion this year—chewing through nearly 1 percent of all global electricity production. Much of this is wasted by a grossly inefficient piece of hardware: the power amplifier, a gadget that turns electricity into radio signals.
The versions of amplifiers within smartphones suffer similar problems. If you’ve noticed your phone getting warm and rapidly draining the battery when streaming video or sending large files, blame the power amplifiers. As with the versions in base stations, these chips waste more than 65 percent of their energy—and that’s why you sometimes need to charge your phone twice a day.
Now an MIT spinout company called Eta Devices, based in Cambridge, Massachusetts, cofounded by two MIT electrical engineering professors, Joel Dawson and David Perreault, say they have cracked the efficiency problem with a new amplifier design.
It’s currently a lab-bench technology, but if it proves itself in commercialization, which is expected to start in 2013—first targeting LTE base stations—the technology could slash base station energy use by half. Likewise, a chip-scale version of the technology, still in development, could double the battery life of smartphones.
“There really has been no significant advance in this area for years,” says Vanu Bose, founder of Vanu, a wireless technology startup. “If you get 30 to 35 percent efficiency with today’s amplifiers, you are doing really well. But they can more than double that.”
Power amplifiers use transistors that consume power in two basic modes: standby mode and output signal mode when sending out pulses of digital data. The only way to improve their efficiency is to use the lowest amount of standby power possible. But making sudden jumps from low-power standby mode to high-power output mode tends to distort signals, so existing technologies keep standby power levels high, wasting electricity.
“It means you are pulling a lot of energy just to keep the thing on,” says Dawson. And the more data you need to send, the worse it gets. “With high data rate communication, you wind up needing far more standby power than signal power. This is why the phone is warm,” he says.
The new advance is essentially a blazingly fast electronic gearbox. It chooses among different voltages that can be sent across the transistor, and selects the one that minimizes power consumption, and it does this as many as 20 million times per second. The company calls the technology asymmetric multilevel outphasing.
The problem they are attacking affects not only when you are literally transmitting something, but also when you are receiving. In the latter situation, the amplifier is busy as the device continually sends out messages confirming the receipt of packets—collections of bits that make up a unit of Internet communications—or alerting the network when packets are missing. “The transmitter is very active, even when you are downloading a YouTube video—not many consumers realize that,” Dawson says.
That is why reducing the communications involved in correcting for missing packets is the aim of another bandwidth-expanding and energy-saving technology, known as network coding (see “A Bandwidth Breakthrough”).
Eta Devices, funded by $6 million from Ray Stata, cofounder of Analog Devices, and his venture firm, Stata Venture Partners, is expected to formally launch its product in February at Mobile World Congress in Barcelona, Spain. The initial market will be in the developing world, where 640,000 diesel-powered generators are used to power base stations, chewing through $15 billion worth of fuel per year.
But the company is aiming at the massive smartphone market. It hopes that its work on a smartphone chip will ultimately lead to a single power amplifier that can handle all of the different modes and frequencies used by the various global standards, such as CDMA, GSM, and 4G/LTE. (Inside an iPhone 5, for example, there are currently five such chips.)
But the base station application is an important one by itself. In large base stations, the power amplifier typically takes 67 percent of the power, with another 11 percent for air-conditioning, or a total of 78 percent of electricity consumption. The new amplifier would reduce overall power consumption by half, says Mattias Astrom, the company’s CEO. As the global demand for data-rich communications surges, about a million new macro base stations are being deployed each year, most of them with LTE technology, he says.
The technology’s indirect savings could include eliminating air-conditioning in big base stations and reducing the size of backup power systems. “There are a lot of secondary effects that are really important,” says Astrom, whose last company, a mapping company called C3, was sold to Apple. While Eta Devices has been quiet in recent months, “now we are extremely confident about what we have here,” he says.
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