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A novel, large-signal behavioral modeling methodology for Gallium Nitride (GaN) high-electron-mobility transistors (HEMTs), based on the canonical piecewise-linear (CPL) functions, is presented in this paper. The proposed new model employs the poly-harmonic distortion (PHD) model framework, making use of the CPL functions for interpolation of the amplitude of the dominant input signal. The CPL method is also applied to the quadratic PHD (QPHD) model framework, allowing for application to devices operating under high (greater than 3 dB) compression levels. Compared with the standard PHD/QPHD models, which require lengthy tables of parameter values to account for the varying large signal input power(s), the models described in this paper are able to predict transistor behavior at different levels of input power, from the linear region to the strongly nonlinear region (where gain compression exceeds 1 dB), with one single set of model coefficients. The basic theory of the proposed model for both RF and dc responses is provided in the paper. The proposed modeling technique is validated through simulated and experimental data from separate 6 W and 10 W GaN HEMT devices, over a wide range of load conditions and power levels. In addition, a two-dimensional polynomial-based model is used for performance comparison, with the proposed method providing comparable accuracy while requiring significantly fewer model coefficients.

In this work, the properties of a two-tone signal driven concurrent power amplifier (CPA) are analyzed extensively. Firstly, the characteristics of two-tone signals are discussed to explain the nonlinearity and efficiency of two-tone signal driven CPA. Secondly, a method of how to solve the efficiency of a two-tone signal driven CPA is proposed in this paper with a detailed calculation procedure and complete theory. Finally, a general empirical expression to calculate the drain efficiency (DE) of CPA versus the frequency ratio and the amplitude ratio of the two carriers is proposed. Simulation results and experimental verifications are given to validate the proposed analytical formulation to predict the efficiency of CPAs when driven with balanced or imbalanced two-tone signals.

In this paper, an analytical design space of power amplifiers (PAs) including the Class-A/B/J continuum for dynamic load modulation (DLM) at the current generator plane (CGP) is proposed based on the theory of load modulated (LM) continuous Class-B/J PAs. By introducing a biasing operation factor ρ, the theory of DLM PAs provides an analytical design space for all the operation modes from Class-B/J mode to Class-A mode. The analytical design space of DLM PAs shows that high efficiency is maintained at a large dynamic range of output power back-off (OPBO) with a purely resistive load modulation at the CGP when Class-B/J mode is performed. For deep Class-AB mode, the analytical design space of the DLM PAs shows that a combination of resistive and reactive load modulation at the CGP is used to maintain the high efficiency at the OPBO. The effectiveness of the proposed analytical design space is validated by load-pull measurements of a bare-chip gallium nitride (GaN) device.