Design and Miniaturization of a 3.1–5.5-GHz Fully Distributed Efficient Power Amplifier MMIC in GaN-on-SiC HEMT Technology

This article presents the design and miniaturization of a wideband monolithic microwave integrated circuit (MMIC) fully distributed efficient power amplifier (FDEPA). Distributed structure arrangement has been applied not only on the auxiliary power amplifier (PA) but also for the main PA. Hence, complicated and bandwidth-limited input matching networks (IMNs) and phase alignment networks are replaced by artificial transmission lines (ATMLs) to simplify the design and save the chip area. At the same time, due to the wide bandwidth characteristic of the distributed main PA, the power back-off (PBO) bandwidth shows good results compared with the conventional single common-source PA arrangement. Besides, a compact wideband on-chip quadrature hybrid power splitter is employed to achieve reasonable power division and phase control. As a proof of concept, an FDEPA prototype has been designed and fabricated in a commercial 0.25-μm GaN-on-SiC process. The chip size is only 3.6 mm×2.55 mm with all the necessary components. From the measurement results, throughout the working band of 3.1-5.5 GHz (56% fractional bandwidth), 40.3-41.6 dBm saturation output power (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>sat</i></sub>), namely 1.16-1.58 W/mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> power density are achieved. The associated saturation drain efficiency (DE) is around 46%-55.4% and the 9-dB PBO DE is around 30.3%-47.2%. Under 100-MHz orthogonal frequency division multiplexing (OFDM) signal excitation with 8.5-dB peak-to-average power ratio (PAPR), 29.3%-44.5% average DE has been observed for the whole operating band, while the adjacent channel power ratio (ACPR) is better than -46.2 dBc with the digital pre-distortion (DPD).