MOSFETs used in cellular and other PAs are virtually 100% discrete RF power transistors.
The laterally diffused metal-on-silicon (LDMOS) FETs are the most popular type.
Freescale Semiconductor is a leader here, with a wide range of devices.
The company’s recent products include the MRF8S9100H/HS, which operates in the
920- to 960-MHz range. It’s designed for class AB or C operations in GSM/EDGE systems.
It can deliver 45-W average power, a gain of 19.1 dB, and an efficiency of 44%. The
MRF8S18120H/HS is made for the 1800- to 1900-MHz bands, where it can deliver 46-W
average power with an efficiency of 42% (see the figure).
But for the higher power levels needed in more rugged applications, gallium-nitride
(GaN) transistors are gaining converts. They offer higher power density, higher gate-todrain
breakdown voltages, and higher operating voltages. In addition, they can operate at
higher junction temperatures. Some deliver up to 100 W in the 1- to 3-GHz range.
Nitronex and NXP offer such devices. BC Systems supplies
complete power amplifiers with those power and
frequency ranges. GaN devices are seen as gradually
replacing traveling-wave-tube (TWT) vacuum tube
amps in some high-power microwave applications
such as in satellites.