High efficienct, linear power amplifiers are a key component for digital modulated signal system. To reduce power consumption, the power amplifier has to be operated near saturation region for high efficieny where amplitude and phase distortion significantly increase, resulting in increased intermodulation distortion.
A simple method to achieve low IMD distortion, the power amplifier operate in several dB back-off from the power saturation point. But in this method the efficient is low. The proposed predistortion circuit consists of only one NMOSFET and bias circuit. Because of its simple circuit, the proposed linearizer can fabricate on integrated circuit. The predistortion linearizer generate a transfer characteristic that is the oposite of the power amplifier saturation characteristic in both magnitude and phase, which provide positive amplitude and negative phase deviations with increase of input power and can compensate AM to AM and AM to PM distortion of power amplifier. The AM-AM, AM-PM distortion is the main cause of IMD distortion. So, applying this proposed linearizer, we can expect the increasing of linearity.
With applying proposed linearizer to power amplifer, the IMD is reduced about 8dBc and ACPR is reduced about 5dBc compared with without proposed linearizer circuit case.
