On the design techniques to improve self-heating, linearity, efficiency and mismatch protection in broadband HBT power amplifiers

InGaP/GaAs Heterojunction Bipolar Transistors (HBTs) are attractive for implementing microwave circuits such as power amplifiers (PAs) due to their high electron mobility, high-current gain, low base resistance, low-loss semi-insulating substrate, better linearity, and high breakdown voltage. A novel design of composite transistors for compensation of InGaP/GaAs HBT self-heating effect and enhancement of InGaP/GaAs HBT linearity has been proposed. This self-heating compensation theory and enhancement of linearity technique can be used in power cell with unnoticeable increase of chip area as well.; A multi-band power amplifier module (PAM), comprised of an InGaP/GaAs HBT monolithic microwave integrated circuit (MMIC) broadband power amplifier and a tunable multi-band output matching circuit is proposed and demonstrated. The 3-stage MMIC broadband power amplifier is realized by using the novel HBT structure and layout, adopting power gain predistortion at the first stage, and optimizing the distribution of power gain among stages. The output matching circuit is implemented with parallel LC tank circuits using PIN diodes to control the inductor value. This multi-band PAM offers advantages of tunable frequency band, low insertion loss, small size and high linearity.; InGaP/GaAs HBTs are widely used as power amplifiers in wireless communications in the past decade. However, GaAs devices are more prone to damage under mismatch conditions than silicon devices due to a lower thermal conductivity and lower melting temperature of the material, making it prone to lattice damage from high current and voltage stress. A protection circuit is proposed to make the power amplifiers safe under mismatch conditions with minimum chip area penalty and power insertion loss covering a broad frequency range.; The power added efficiency is proportional to the output power if the power amplifiers work in Class A mode. However, since the power amplifiers seldom works at saturation power in most of wireless communication systems, the overall efficiency of the power amplifier is degraded greatly. In order to improve the efficiency of the power amplifier within a wide power range, a dynamic biasing control circuit is proposed to improve the battery life.