A 2.4–6 GHz Broadband GaN Power Amplifier for 802.11ax Application

This paper presents a 2.4-6 GHz highly integrated broadband GaN power amplifier (PA) with three stages for 2.4-/5-GHz dual-band 802.11ax application. A compact external output matching network is introduced to realize broadband output matching, while reducing the loss of the output matching network and saving the chip area. A novel topology of coupled resonators is exploited for the broadband inter-stage matching to cover the 802.11ax bands from 2.4 to 6 GHz. In the proposed topology, the coupling between the primary and secondary resonators is through a series inductor and a series capacitor. Compared with other conventional coupled resonators, the proposed topology produces an additional complex pole, further extending the bandwidth. The PA was designed and fabricated in Wolfspeed 0.25- μm GaN-on-SiC technology. The implemented PA achieves a saturated output power (P_sat) of 35.2-36.3 dBm with a maximum power added efficiency (PAE) of 38-53% from 2.4 to 6 GHz. When tested with an 80-MHz, 256-quadratic-amplitude modulation (QAM) 802.11ax signal, the PA delivers an average output power of 27.1 and 25.7-27.2 dBm with a PAE of 20.9% and 18.4-24.6% in the 2.4-GHz and 5-GHz wireless local area network (WLAN) bands, respectively, while meeting the specification of error vector magnitude (EVM) below -32 dB.

I. Introduction

Recently, the accelerating growth of smartphones and mobile devices is propelling wireless communications towards higher data rate. Currently, as the successor to IEEE 802.11ac, the emerging IEEE 802.11ax introduces OFDMA and utilizes smaller sub-carrier spacing to improve overall spectrum efficiency and boost the data rate. The data rate of 802.11ax is expected to reach 10 Gb/s, in order to meet the tremendous demand for high data rate applications, such as interactive and high-definition video. However, the wide bandwidth and complex modulation scheme of 802.11ax result in large peak-to-average power ratio (PAPR), requiring a large back-off for power amplifier (PA) to meet the stringent EVM requirement, thus reducing the power efficiency. Since GaN HEMT device exhibits high breakdown voltage and high power density, GaN PA is a good candidate for 802.11ax access point (AP) with a large coverage range.