High-efficiency power amplifier could bring 5G cell phones

Fifth-generation, or 5G, mobile devices expected around 2019 will require improved power amplifiers operating at very high frequencies. The new phones will be designed to download and transmit data and videos faster than today's phones, provide better coverage, consume less power and meet the needs of an emerging "Internet of things" in which everyday objects have network connectivity, allowing them to send and receive data.

Power amplifiers are needed to transmit signals. Because today's cell phone amplifiers are made of gallium arsenide, they cannot be integrated into the phone's silicon-based technology, called complementary metal-oxide-semiconductor (CMOS). The new amplifier design is CMOS-based, meaning it could allow researchers to integrate the power amplifier with the phone's electronic chip, reducing manufacturing costs and power consumption while boosting performance.

"Silicon is much less expensive than gallium arsenide, more reliable and has a longer lifespan, and if you have everything on one chip it's also easier to test and maintain," said Saeed Mohammadi, an associate professor of electrical and computer engineering at Purdue University. "We have developed the highest efficiency CMOS power amplifier in the frequency range needed for 5G cell phones and next-generation radars."

Findings are detailed in two papers, one to be presented during the IEEE International Microwave Symposium on May 24 in San Francisco, authored by former doctoral student Sultan R. Helmi, who has graduated, and Mohammadi. They authored another paper with former doctoral student Jing-Hwa Chen to appear in a future issue of the journal IEEE Transactions on Microwave Theory and Techniques.

The amplifier achieves an efficiency of 40 percent, which is comparable to amplifiers made of gallium arsenide.

The researchers created the new type of amplifier using a high-performance type of CMOS technology called silicon on insulator (SOI). The new amplifier design has several silicon transistors stacked together and reduces the number of metal interconnections normally needed between transistors, reducing "parasitic capacitance," which hinders performance and can lead to damage to electronic circuits.

"We have merged transistors so we are using less metallization around the device, and that way we have reduced the capacitance and can achieve higher efficiencies," Mohammadi said. "We are trying to eliminate metallization between transistors."

The new amplifiers could bring low-cost collision-avoidance radars for cars and electronics for lightweight communications microsatellites.

The CMOS amplifiers could allow researchers to design microsatellites that are one-hundredth the weight of today's technology.

Three U.S. patents related to the amplifier have been issued. The research was funded partially by the U.S. Defense Advanced Research Projects Agency.

The researchers are working on a new version of the amplifier that is twice as powerful. Further work will be needed to integrate the amplifier into a cell phone chip.