Larry Leighton

LDMOS RF Power Transistors and Their Applications

The recent surge in wireless communication services has created a huge demand for cost-effective, high gain, ultra-linear high power RF transistors for use in base station power amplifiers. Laterally diffused metal-oxide-semiconductor (LDMOS) transistors have been proven to be very popular for these applications. They have superior RF performance compared to bipolar transistors and are highly cost-effective compared to their GaAs counterparts. The first section of this chapter provides an insight into developing an LDMOS RF power transistor and its applications in the cellular communications industry. The chapter discusses the physics of the operation of transistors and highlights the attributes of the technology that helps in highly linear applications. It also discusses circuit considerations for the design of a stable wideband amplifier using MOS technology. There are many advantages of LDMOS technology compared to the vertical MOS structures. LDMOS transistor has high-doped p-type sinker diffusion, which is used to ground the source to the substrate. Two applications of LDMOS are frequency division multiple access (FDMA), used for standard analog cellular applications; and time division multiple access (TDMA), where multiple users can share the RF carrier on a time slot basis. There is a need for concentrated efforts by RF power transistor designers to develop a robust device model that enables accurate and quick designs for system designers and also aids in the development of ultra-linear, highly efficient, next generation devices.