Improved Linearity and Efficiency of 5-GHz HBT Power Amplifier Using Transformer-Based Second Harmonic Trap Network

This letter presents an improved linear and efficient heterojunction bipolar transistor (HBT) power amplifier (PA) for mobile applications using a newly proposed transformer (TF)-based second harmonic trap that only terminates the second harmonic, without affecting the fundamental frequency. Compared to the configuration without the second harmonic trap, the PA with the proposed second harmonic trap has improved linearity, gain, and PAE. The PA is implemented in a 2- ${\mu }{\text {m}}$ InGaP/GaAs HBT process, and the input and output TFs are built on a nine-layer printed circuit board. The fabricated PA achieves a small-signal gain of 23.3 dB, saturated output power of 33.5 dBm, and peak PAE of 45.9% at a collector voltage of 4.5 V over 5.15–5.925 GHz under continuous-wave signal. A new radio (NR) 100-MHz QPSK CP 273 RB signal with a peak-to-average power ratio (PAPR) of 10.7 dB is used to test linearity. The PA achieves improved efficiency from 5.8%–9% to 6.4%–11.5% in the linear output power region which meeting adjacent channel leakage ratio (ACLR) of −33 dBc.