A new highly efficient power amplifier (PA) based on silicon-on-insulator (SOI) CMOS could help to make possible next-generation cell phones, low-cost collision-avoidance radar for cars and lightweight microsatellites for communications, say researchers at Purdue University.
Fifth-generation (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 existing 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.
Because existing cell-phone power amplifiers for transmitting signals are made of gallium arsenide (GaAs), they cannot be integrated into the phone's silicon-based complementary metal-oxide-semiconductor (CMOS) technology. Since the new amplifier design is CMOS-based, 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," says Saeed Mohammadi, 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." The amplifier achieves an efficiency of 40%, comparable to amplifiers made of gallium arsenide, it is reckoned.
Findings are detailed in two papers, one to be presented on 24 May at the IEEE International Microwave Symposium (IMS2016) in San Francisco, authored by former doctoral student Sultan R. Helmi together with Mohammadi. They also authored another paper with former doctoral student Jing-Hwa Chen, to appear in an issue of IEEE Transactions on Microwave Theory and Techniques.
The researchers created the new type of amplifier using silicon-on-insulator (SOI) CMOS technology. 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," says Mohammadi. "We are trying to eliminate metallization between transistors."
The new amplifiers could also bring about low-cost collision-avoidance radars for cars and electronics for lightweight communications microsatellites. Specifically, the CMOS amplifiers could allow researchers to design microsatellites that are one-hundredth the weight of existing technology.
The research was funded partially by the US Defense Advanced Research Projects Agency (DARPA), and three US patents related to the amplifier have been issued.
The researchers are currently 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.
