To the 3G handset user, the objectives are straightforward: I want speed and reliability. I want fast data rates and a robust connection. I want my device to work wherever I go, no matter how far from the cell tower or which part of the device I am holding. And I want great talk time. All of these 3G needs are enabled by gallium arsenide (GaAs) power amplifiers.
When we look at whether CMOS can replace GaAs today in meeting all of these needs, the answer, clearly, is no. Let's start with quality of service anywhere in the cell. Handsets today generally transmit in a wide range of power. Higher power levels are needed to ensure a robust connection, not only when the user is farthest from the tower, but also when the path is blocked by walls, ceilings, trees and any other obstructions, like in a large metropolis. There are no CMOS PAs in the market that are capable of delivering the sort of linear output power that is needed from today's popular handsets. To do so, they would have to make compromises that will diminish the end-user experience.
Imagine you're sitting in a restaurant in the middle of New York, celebrating with friends, and you want to send a picture to a friend who was unable to attend. If your handset cannot transmit at the highest power levels, transmitting the pictureif it works at allwould take what would seem to be an eternity. No consumer wants to purchase a phone that restricts them from using all the cool applications that have been loaded onto the phone. It's all about being able to use your handset wherever and whenever you want it, and for whatever application you wish.
When it comes to 3G power amplifiers and their impact on the user experience, perhaps nothing is more important than talk time. As the last amplification stage in the transmit chain, the PA carries a major burden: it must deliver high output power and do so efficiently. GaAs is a far better process technology than CMOS for delivering linear power. Recent GaAs PAs are achieving close to 45 percent efficiency while meeting all spectral requirements. After all, what good is a mobile device if you have to recharge after 45 minutes of use, or worse, stand near a power outlet to use it? Moreover, CMOS inherently cannot match the ruggedness of GaAs in this environment.
Lastly, while the cost per unit area of CMOS is in many cases less than that of GaAs, the total cost of design, development and implementation needs to be considered. GaAs technology has matured significantly over time, so that the process and simulation toolkits have advanced greatly for designing complex components like high-power amplifiers for complex modulations. This allows for shorter design cycle times.
At Anadigics, we believe GaAs is the best process technology choice for giving our customers what they need in their 3G handsets. It carries the load today in 3G and will be the technology of choice as we march towards 4G. Looking farther out, CMOS will undoubtedly play a role. But, for the near term, GaAs wins the day.
Mario Rivas is the president and CEO of Anadigics Inc. (Warren, N.J.).
See other articles in this Point/Counterpoint series:
Point/Counterpoint: Is CMOS right for 3G handset PAs?
CMOS history repeating again in power amplifiers
CMOS is the right technology for 3G handset PAs