100-300 GHz Power Amplifiers: Transistor Limits, Circuit Topologies

The 100-300 GHz band may prove useful for high-resolution radar imaging and for high-capacity point-point MIMO backhaul links; the transceivers therein may use linear arrays with ~0.1-1W output power per channel, or 2D arrays with ~10-100mW output power per channel. Focusing primarily on InP HBT technologies, I will first consider factors setting the transistor maximum and minimum output voltage and current density, and high-frequency constraints on multi-finger transistor layout and the resulting current limits on high-frequency output power. I will then describe 100-300 GHz PA design techniques, including multi-finger transistor cell design, PAE and added power invariance, electrothermal instability, and adaptive class-AB biasing. I will compare the relative advantages of corporate, segmented transformer, sub-quarter-wave coupled-line, stacked and cascaded power-combining, and will explore the close relationship between transformers and coupled lines. Design examples include a ~27 dBm 150 GHz design with 14.9% PAE, and a design producing 78mW at 220 GHz with 18% PAE.