Vector-Sum Phase Shifter Design for Analog Predistortion in an FR3 Band Power Amplifier Using GaAs HBT

This paper presents a power amplifier (PA) for cellular handsets operating in the frequency range 3 (FR3) band that employs distortion compensation. The compensation circuit uses a vector-sum phase shifter in which phase is controlled by the envelope amplitude, flattening the PA’s AM/PM characteristic. The PA was fabricated using a GaAs HBT process. Continuous-wave (CW) measurements at 8 GHz achieved flat AM/PM behavior and peak gain and power-added efficiency (PAE) of 32 dB and 42%, respectively. Measurements with modulated signals yielded an adjacent-channel leakage ratio (ACLR) of −37.4 dBc and an error vector magnitude (EVM) of −34.5 dB, representing 7 dB improvements relative to operation without distortion compensation.