High third-order-intercept series-FET driver power amplifier [Application Notes]

An amplifier is called linear when the output power increases linearly with the input power. As input power increases, the amplifier transfer function becomes nonlinear, and a stage is reached where the output power does not increase with the input power. This happens because of transistor current and voltage clipping and the variations of transistor transconductance and junction capacitances with input RF power. One of the measures of nonlinearity of amplifiers is intermodulation distortion (IMD). When more than one carrier frequency is present in a nonlinear amplifier, multiple sidebands will be generated as intermodulation products due to mixing in the nonlinear device 1]-8].