CMOS PA design at mm-wave frequencies

As the mm-wave frequency range gains in importance, the design of PAs at these frequencies has become crucial. CMOS is the technology of choice for high-volume communication products. MIMO and beamforming are enablers to achieve the required link-budget and throughput. But all this puts more pressure on the required specifications of the power amplifier, such as linearity, efficiency, output power, footprint and more. This presentation will discuss the challenges of designing a CMOS power amplifier at mm-wave frequencies. Transistor layout optimization towards gain, stability and output power will be discussed in much detail, as well as power combining and device stacking as these are crucial to achieve sufficient output power from a low-voltage technology. At the architecture level, many options lie ahead such as polar, envelope tracking, outphasing, Doherty, … They will be reviewed in detail and their pros and cons for mm-wave operation will be presented. Many examples will be presented in 28nm and 40nm CMOS, covering a frequency range from 28GHz up to 85GHz.