High performance SiGe HBT power unit-cell for S-Band open collector adaptive bias power amplifier design

A SiGe heterojunction bipolar transistor (HBT) power unit-cell for S-Band high efficiency linear power amplifier with an open collector adaptive bias linearizer was designed and fabricated in this paper. The unit-cell was investigated in both electrical and thermal performances and 34 unit-cells were then combined as a power device for output stage. An adaptive linearizer for the output stage was constructed with an open collector HBT bias circuit and improved the power gain (G_p), output 1 dB compressed power (OP_{1 dB}), power added efficiency (PAE), and output third-order intermodulation point (OIP₃) when compared to those of traditional adaptive bias circuit. The measured power amplifier achieved a G_p of 13 dB, an OP_{1 dB} of 22 dBm with a PAE of 28.6%, and an OIP₃ of 31.4 dBm. Compared to traditional adaptive bias technique, the proposed linear power amplifier improved the output power of 2 dB, PAE (at P_{1 dB}) of 8.6% and OIP₃ of 3.4 dB. The fabricated die size, including pads, is less than 1.44 mm².