Class-J23 Power Amplifiers

Recently, class-J₂ operation mode has been proposed in the literature for high-efficiency power amplifier (PA) design. It has been shown that the output power (<inline-formula> <tex-math notation="LaTeX">${P_{\text {out}}}$ </tex-math></inline-formula>) of a class-J₂ PA can be 1.5 dB higher than <inline-formula> <tex-math notation="LaTeX">${P_{\text {out}}}$ </tex-math></inline-formula> of a class-J counterpart, whereas the theoretical drain efficiency of the class-J₂ mode can be as high as 83%. This paper is devoted to introduce and characterize the class-J₂₃ mode of operation, which is the generalized form of the class-J₂ mode and provides a new design space to realize highly efficient PAs. In this new PA mode, the third-harmonic voltage is also included in the drain voltage of the transistor to increase the drain efficiency up to 95.4% in theory. Design space is explored for the class-J₂₃ mode, and formulations are derived for the output power, drain efficiency, load impedance at the fundamental frequency, and the second- and third-harmonic load impedances. It is shown that the output power and drain efficiency of the class-J₂₃ mode remain constant for coupled variations of the fundamental and third-harmonic impedances, while the second-harmonic impedance is open-circuited. To validate the theoretical predictions, a proof-of-concept fully integrated PA is fabricated in a 0.25-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> GaAs pHEMT technology. The prototype PA features an average output power of 30.7 dBm and drain efficiency of 68% in a 2.5–3.6-GHz bandwidth.