truction of the base area of the transistor. In CMOS devices this is achieved by reducing the thickness of the base to micrometres or submicrometres but this reduces the breakdown voltage of the device. The two design objectives, higher voltage for lower noise and a thinner base for higher electron mobility are therefore directly opposed. At least two vendors are actively pursuing the use of CMOS for LTE user devices but whether a cost performance crossover point has been reached is still open to debate. Low-voltage PA operation also is a direct contributor to PA bandwidth restriction. Because it is output power that is specified, low supply voltages force the use of higher currents in the PA transistors. This only happens by designing at low impedances, significantly below the nominal 50 ohms of radio interfaces. Physics requires that impedance value shifts happen with bandwidth restrictions: larger impedance shifts involve increasingly restricted bandwidths. At a fixed power, broadband operation and low-voltage operation are in direct opposition. Gallium arsenide in comparison allows electrons to move faster and can therefore gener- ally deliver a better compromise between efficiency, noise and stability, a function of input impedance. However, the material has a lower thermal conductivity than CMOS and is more brittle. This means that it can only be manufactured in smaller wafers, which increases cost. The material is less common than silicon, the world's most common chemical element, and demands careful and potentially costly environmental management. As at today, gallium ar- senide remains dominant in 3G user devices for the immediately foreseeable future and is still the preferred choice for tier 1 PA vendors. Gallium nitride, already used in base station amplifiers is another alternative with electron mobility equivalent to GaAs but with higher power density, allowing smaller devices to handle Wireless User Hardware more power. Gallium nitride is currently used in a number of military applications where ef