High efficiency open collector adaptive bias SiGe HBT differential power amplifier

A high efficiency SiGe HBT differential power amplifier with an open collector adaptive bias was successfully demonstrated. A novel linearizer consists of an open collector heterojunction bipolar transistor bias circuit and an MOS feedback diode was proposed, which achieved better power added efficiency (PAE) than that of traditional adaptive bias circuits. The size effect of linearizer was investigated and the impedance ratio (R ₁/R₂) between the linearizer and the main amplifier was optimized by the factor of 3. The measured differential power amplifier achieved an output 1-dB compression point (P_{1 dB}) of 18.7 dBm with PAE of 31.2, the output second order intermodulation point (OIP₂) of 59 dBm, and third-order intermodulation point (OIP₃) of 28 dBm. Compared to traditional adaptive bias technique, the proposed linearizer power amplifier effectively improved the PAE. The fabricated die size including pads is less than 0.925 mm² and suitable for highly integrated linear drive amplifier.