were also commonly used in the past, up until they were replaced by power MOSFETs, particularly LDMOS transistors, as the standard technology for RF power amplifiers by the 1990s,BJT are still commonly used for high frequency power amplifiers. Generally speaking, solid-state power amplifiers (SSPA) contain four main components: input, output, amplification stage and power supply.

MOSFET transistors and other modern solid-state