Design of a Highly Efficient Class-F GaN MMIC Power Amplifier Using a Multi-Function Bias Network and a Harmonic-Isolation L-C Resonator

This paper proposes a new method to design compact and high-efficiency Class-F GaN microwave monolithic integrated circuit (MMIC) based power amplifiers (PAs). Closed-form design equations are derived to synthesize a multi-function bias branch sub-network (BBSN) and a harmonic-isolation matching branch sub-network (MBSN), which together form a network that is capable to satisfy the Class-F load condition from fundamental up to the
$4^{th}$
harmonic frequency. These equations further assist in analyzing the impact of the finite inductor quality factor on the passive efficiency of the proposed network, yielding design choices that offer both reduced chip size and passive loss. For validation, the proposed method is applied to design a C-band high-efficiency PA in a commercial 0.25
$\mu {\mathrm{ m}}$
GaN-on-SiC HEMT process. Measurements under pulsed continuous-wave stimulation reveal, the proposed PA is capable of providing saturation output power of 38.5-39.1 dBm and excellent power-added efficiency (PAE) of 61%-70% over 5.3-5.9 GHz with a chip size of
$1.5\times2.2$
mm2. Moreover, when excited by a 100 MHz 256-QAM signal, the amplifier can offer an average PAE of 33.1-38.2%, adjacent channel power ratio (ACPR) of
$ < -35$
dBc, error vector magnitude (EVM) of 2.7-3.7%, without applying any digital pre-distortion (DPD).