10
Power Amplifier Design Fundamentals
Generally, the power amplifier design requires accurate active device modeling, impedance matching depending on the technical requirements and operation conditions, stability in operation, and simplicity in practical implementation. The quality of the power amplifier design is evaluated by realized maximum power gain under stable operation condition with minimum amplifier stages, and the requirement of linearity or high efficiency can be considered where it is needed. For a stable operation, it is necessary to evaluate the operating frequency domains where the active device may be potentially unstable. To avoid the parasitic oscillations, the stabilization circuit technique for different frequency domains (from low frequencies up to high frequencies close to the device transition frequency) is discussed. The key parameter of the power amplifier is its linearity, which is very important for many wireless communication applications. The relationships between the output power, 1-dB gain compression point, third-order intercept point, and intermodulation distortions of the third and higher orders are given and illustrated for different active devices. The device bias conditions that are generally different for linearity or efficiency improvement depend on the power amplifier operation class and the type of the active device. The bias circuits for the voltage-controlled metal-oxide-semiconductor field-effect transistor (MOSFET) devices are simple ...
