Impedance transformations over large bandwidth are difficult to realize, thus most wideband amplifiers use 50 Ω output loading. Transistor output power is then limited to
P_{out} le frac{(V_{br} - V_k)^2}{8Z_o}
V_{br} is defined as the breakdown voltage
V_k is defined as the knee voltage
and typically Z_o = 50Omega,
The loadline method is often used in RF power amplifier design.