A 2.5 Watt 2.6 GHz HBT Power Amplifier Using Transformer-Based Matching Networks

A three-stage power amplifier (PA) based on commercial GaAs HBT technology is presented for 5G NR band n41. The PA's front-stage driving circuitry adopts a single-ended cascaded amplification topology, while the final stage utilizes transformer (TF)-based matching networks (MNs) for power division and combination, which effectively improve the return loss and extend the bandwidth meanwhile addressing the challenge of interstage matching with relatively large impedance transformation ratio (ITR). The global stability of the PA is ensured by the addition of series-RC negative feedback networks. Experimental results demonstrate that the small-signal gain exceeds 33.9 dB across 2.5-2.7 GHz, with saturated output power
$(\mathrm{P}_{\text{sat}})$
fluctuations of 33.8-34.2 dBm, peak power-added efficiency (PAE) of 33.3%, and the adjacent-channel power ratio (ACPR) below -39.5 dBc at an output power
$(\mathrm{P}_{\text{out}})$
of 26 dBm.