Cambridge, UK: Cambridge University Press. The Design of CMOS Radio-Frequency Integrated Circuits. CS1 maint: uses authors parameter ( link) The loadline method is often used in RF power amplifier design. Transistor output power is then limited to Impedance transformations over large bandwidth are difficult to realize, so conventionally, most wideband amplifiers are designed to feed a 50 Ω output load. LDMOS-based RF power amplifiers are widely used in digital mobile networks such as 2G, 3G, and 4G. RF power amplifiers using LDMOS (laterally diffused MOSFET) are the most widely used power semiconductor devices in wireless telecommunication networks, particularly mobile networks. The transmitter–receivers are used not only for voice and data communication but also for weather sensing (in the form of a radar). Among these applications, driving transmitter antennas is most well known. The basic applications of the RF power amplifier include driving to another high power source, driving a transmitting antenna and exciting microwave cavity resonators. Tubes are mechanically fragile but electrically robust – they can handle remarkably high electrical overloads without appreciable damage. Although mechanically robust, transistors are electrically fragile – they are easily damaged by excess voltage or current. MOSFET transistors and other modern solid-state devices have replaced vacuum tubes in most electronic devices, but tubes are still used in some high-power transmitters (see valve RF amplifier). Bipolar junction transistors 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, due to the superior RF performance of LDMOS transistors. The earliest MOSFET-based RF amplifiers date back to the mid-1960s. Modern RF power amplifiers use solid-state devices, predominantly MOSFETs (metal-oxide-semiconductor field-effect transistors). The class D amplifier is not often used in RF applications because the finite switching speed of the active devices and possible charge storage in saturation could lead to a large I-V product, which deteriorates efficiency. Among the switch-mode classes are class D, class F and class E. Operating the active device as a switch results in higher efficiency, theoretically up to 100%, but lower linearity. The previously named classes become more efficient, but less linear, in the order they are listed. The bias at the input determines the class of the amplifier.Ī common trade-off in power amplifier design is the trade-off between efficiency and linearity.
In these classes the active device is used as a controlled current source. Some classes are class A, class AB, class B, class C, which are considered the linear amplifier classes. Many modern RF amplifiers operate in different modes, called "classes", to help achieve different design goals.