A Feedback Technique to Compensate for AM-PM Distortion in Linear CMOS Class-F Power Amplifier

An amplitude-phase (AM-PM) linearization technique using a direct drain-gate feedback method in a cascode CMOS amplifier is proposed. This technique consists of a series-connected capacitor and an inductor coupling the residue of the RF signal drain. The coupled RF ac signal to gate node of the common gate stage (CG) prevents the CG stage from entering the triode region at a high output power region. In this respect, the parasitic gate-drain capacitance sustains a constant value, achieving an enhancement in linearity. To verify the superior performance of the proposed technique, a CMOS PA was fabricated using a commercial 0.18 mu m process. The experimental results show that the implemented PA delivers a PAE of 34.2% at an output power of 26.7 dBm for a 10 MHz 3G LTE signal at Band 5/8 (824-915 MHz), and has an improved spectral performance of over 5 dBc.