A 0.8 mm2 Sub-GHz GaAs HBT Power Amplifier for 5G Application Achieving 57.5% PAE and 28.5 dBm Maximum Linear Output Power

This paper presents a comprehensive design of a fully integrated multistage GaAs HBT power amplifier that achieves both linearity and high efficiency within a chip area of 0.855 mm2 for 4G and 5G applications covering the lower frequency band of 700–800 MHz. A novel linearizer circuit is integrated to a dual stage class-AB PA to minimize the AM-PM (Amplitude Modulation-Phase Modulation) distortion generated by the parasitic capacitance at the PN-junction under low bias current condition. The linearized power amplifier is able to operate within a 100 MHz linear operating bandwidth (700-800 MHz) while meeting the adjacent channel leakage ratio (ACLR) specification for 4G and 5G application. The fully integrated PA achieves a wideband efficiency of 57.5% at 28.5 dBm output power. Observing a respective input and output return losses of less than 13 dB and 10 dB, the PA delivers a power gain within the range of 34.0-37.0 dB across the operating bandwidth while exhibiting an unconditional stability characteristic from DC up to 5 GHz. The proposed linearization method paves the way of reducing the complexity of linear and high efficiency PA design which is associated with complicated and high-power consumption linearization schemes.