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MWJ: You’ve left MIT for a start up, what were you thinking?
JD: Well, it’s not just any startup. It’s MY startup. The convergence of events that made this company possible was just too compelling to ignore. The original plan was to be here about a year, and then return to academia. Now we’re 18 months into the journey as a funded company, but we agreed among ourselves to start the company four years ago and we incorporated three years ago, all on the basis of some promising results coming out of my lab at MIT. Now what the technology needs is a sustained, concentrated effort by a world-class team, and we are very fortunate that that team has come together. I would be crazy not to give this project my full attention.
MWJ: How did this all get started?
JD: If you look at history, a lot of the techniques of radio are from the early 20th century; Marconi, Armstrong, etc. Part of the reason these techniques stuck around so long is because they are really fundamentally sound. As great as these techniques are, though, their inventors were laboring under the constraint that they could only use a handful of active devices. Vacuum tubes were expensive in those days, and not very reliable, and so a successful circuit could only use a few. Today, we can specify a billion transistors within a few square millimeters of silicon, and expect all of them to work.
So I got to thinking about what’s the right way to take advantage of all this technology to build better radios. That was the big question I took on as a professor at MIT. The individual projects that I started were more or less united under that theme.
The project that led to our company started when I went to a talk given by Dave Perrault, another faculty member at MIT. Dave is famous for making some of the smallest, most efficient power converters in the world. During his talk, he made a throwaway comment-- “I’m trying to make the power converter really small and as a by-product, you can modulate its output very fast. I have no idea why you would want that, but here it is.” I practically jumped out of my seat. The answer, as any radio researcher would tell you, is that you would build the world’s most efficient radio transmitter. At the time we expected to use a technique called envelope tracking, but as we got deeper into the creative process we came up with Asymmetric Multilevel Out.
MWJ: What exactly is Asymmetric Multilevel Outphasing (AMO) phasing?
JD: Ever drive a manual transmission? Think about the gearbox. Imagine you had no ability to look ahead, and so never knew how steep an upcoming hill might be (suppose also that you had really slow reflexes). One strategy would be to stay in first gear the entire time and, let RPMs be as low or as high as they need to be. That’s really inefficient, and your gas mileage would suffer. You need gears one through five to make the engine run smoothly given the varying terrain. One of the incumbent technologies – envelope tracking—takes this idea to an extreme. Back to the car analogy, it would be like having a continuous transmission with an infinite number of gears. But for a lot of reasons, envelope tracking winds up not working as well when bandwidth increases. And bandwidth is rapidly increasing. LTE and 4G standards require 20 MHz BW today, and 40 MHz and beyond within the next few years. Envelope tracking is having a hard time keeping up. So with AMO, the idea is to return to the discrete gearbox, and use digital signal processing to keep the signal spectrally clean.
MWJ: Why did it take 10 years to develop this?
JD: Because the starting point was almost philosophical: “How can we use all these transistors to build better radios?” Getting from there to a more focused question-- how can we build the world’s most efficient RF power amplifier? -- took a few years and several projects. The inspiration for this particular project didn’t hit until Dave and I until we connected in 2007. From there, hardware projects are hard, and take a lot of time and effort so it took a while.
MWJ:You make some bold claims about being the world’s most efficient power amplifier – how is that possible?
JD: Yes. And now we’ve been going all around the world with a live demo to prove it. If I had to break down the causes of skepticism, most engineers did not challenge the claim that we would wind up with an efficient solution. What everyone doubted was that, for various reasons, we could get high efficiency and a spectrally clean output signal at the same time. That’s the real trick, and spectral cleanliness is hard when you have abrupt transitions from this “gearbox.”
MWJ: What’s the market opportunity size here?
JD: Two billion phones a year. Our vision is to save a few dollars off the bill of materials for the manufacturer.
MWJ: You’ve said implementing Eta Devices’ technology in mobile base stations is analogous to replacing incandescent light bulbs with much more efficient LED lights. Could you explain what that means?
If you look at the incandescent light bulb, the way that it shows its inefficiency is that it radiates a lot of heat. That heat is wasted energy, and it would be better if that energy came out in the form of light. LED light bulbs reduce the amount of energy wasted as heat by as much as 80% compared to incandescent bulbs. If you compare our transmitter to what is currently deployed, the heat reduction percentage is about the same.
MWJ: Who will benefit from this being in the marketplace? The cost savings potential seems clear, but there are also environmental implications, correct?
JD: The CO2 emissions from the worldwide network of base stations are the equivalent of the output of 15 million cars. We’re talking about cutting that in half. On the infrastructure side, especially in the developing world, they typically use diesel fuel to power the base stations. In India in particular, the need is urgent because in 2014 the Indian government will eliminate its current subsidy for diesel fuel.
On the handset side, everyone is experiencing that their battery doesn’t last all day. And elite users who travel the globe often have to carry extra batteries or two phones. Our vision is to bring improved performance to all users of smart phones.
MWJ: What pieces need to be in place to optimize this for the market? Who will be the first to use your technology and where?
JD: Our biggest challenge is that the whole wireless ecosystem is dominated by just a few powerful players. Until it’s obvious to them that it’s in their best interest to adopt a new technology, they won’t move.
What we have going for us is that we own the IP in this space. This is important, because we are now demonstrating performance that surpasses every other known technique by a large margin. So ultimately the big players have to ask themselves: “How long can we afford to market ourselves as having the second-most efficient transmitters in the world?”
We think the first deployment of our technology will be in the base stations of the developing world.
MWJ: Are there applications for Eta Devices technology beyond base stations?
JD: Absolutely, handsets, WiFi, MRI machines, satellite and military communications, etc. can use this technology. Our vision is that 20 years from now, this is the way that everyone will design radio transmitters.
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