A Ka-Band CMOS Analog Linearizer With Independently Configurable Nonlinear Characteristics Compatible to GaN and CMOS PAs

This article presents an analog linearizer that linearizes multiple power amplifiers (PAs) by configuring target predistortion curves, including tunable slopes for both amplitude modulation (AM)–AM and AM-phase modulation (PM) curves, as well as adjustable critical output power points for each curve. Moreover, general memoryless nonlinear models for analog linearizers are proposed, and a boundary parameter-searching approach based on the error vector magnitude (EVM) gradient optimization is introduced to determine the optimal maximum expansion of gain and phase. Prototype validation involves linearization of both a GaN PA and a CMOS PA. The proposed linearizer is implemented in a 65-nm CMOS process, employing nonlinear inductive techniques and diode-connected methods for continuous adjustments in phase and gain expansion. Matching strategies are discussed to increase the corresponding expansion range while decoupling AM-AM and AM-PM. Gain adjustments are determined to control the critical output power points. The experiment shows that the designed linearizer achieves a gain expansion of over 3.5 dB and a phase expansion exceeding 25° at 35 GHz while consuming approximately 74.2 mW. Modulated signal measurements in four scenarios demonstrate significant EVM improvements. Specifically, for the GaN PA with a signal of 256-quadrature amplitude modulation (QAM) and a 400-MHz bandwidth, EVM can be reduced from 6.6% to 2.9% at 31.3 dBm. For the CMOS PA under the same conditions, EVM can be improved from 6% to 2.8%. Overall, this article provides a universal solution for low-cost linearization of various PAs.