Transistors Are Used In Microwave/RF Power Amplifiers
LDMOS (laterally diffused metal oxide semiconductor transistors are used in microwave/RF power amplifiers. These transistors are often fabricated on p/p+ silicon epitaxial layers. The fabrication of LDMOS devices mostly involves various ion-implantation and subsequent annealing cycles. As an example, The drift region of this power MOSFET is fabricated using up to three ion implantation sequences in order to achieve the appropriate doping profile needed to withstand high electric fields.
Silicon-based LDMOS FETs are widely used in RF power amplifiers for base-stations as the requirement is for high output power with a corresponding drain to source breakdown voltage usually above 60 volts.Compared to other devices such as GaAs FETs they show a lower maximum power gain frequency.
Manufacturers of LDMOS devices and foundries offering LDMOS technologies include TSMC, LFoundry, Tower Semiconductor, GLOBALFOUNDRIES, Vanguard International Semiconductor Corporation, STMicroelectronics, Infineon Technologies, RFMD, Freescale Semiconductor, NXP Semiconductors, SMIC, MK Semiconductors, Polyfet and Ampleon.
RF power amplifiers based on single LDMOS devices suffer from relatively poor efficiency when used in 3G and 4G (LTE) networks, due to the higher peak-to-average power of the modulation schemes and CDMA and OFDMA access techniques used in these communication systems. The efficiency of LDMOS power amplifiers can be boosted using typical efficiency enhancement techniques, for example Dohertytopologies or envelope tracking.