Theory and Design of Class-J Power Amplifiers With Dynamic Load Modulation

• Published in: IEEE transactions on microwave theory and techniques Vol. 60; no. 12; pp. 3778 - 3786
• Main Authors: Andersson, C. M., Gustafsson, D., Yamanaka, K., Kuwata, E., Otsuka, H., Nakayama, M., Hirano, Y., Angelov, I., Fager, C., Rorsman, N.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-12-2012; Institute of Electrical and Electronics Engineers
• Subjects: Amplifiers; Applied sciences; Circuit properties; Electric, optical and optoelectronic circuits; Electronic circuits; Electronic equipment and fabrication. Passive components, printed wiring boards, connectics; Electronics; Energy efficiency; Exact sciences and technology; gallium nitride (GaN); Harmonic analysis; Impedance; Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits; Power amplifiers; Power generation; Radiocommunications; Resistance; silicon-carbide (SiC); Telecommunications; Telecommunications and information theory; Transistors; Transmitters. Receivers; Varactors; Performance evaluation; Dynamic response; Tunable circuit; Output power; gallium nitride (GaN); silicon-carbide (SiC); Transmitter; Power electronics; Static measurement; Power utilization; Load impedance; Reactance; High electron mobility transistor; Varactor diode; High power; Energetic efficiency; Modulation; varactors; Energy efficiency; power amplifiers; Microwave amplifier; Power amplifier; Peak power; Dynamic load
• ISSN: 0018-9480; 1557-9670; 1557-9670
• DOI: 10.1109/TMTT.2012.2221140

A theory for class-J microwave amplifier operation as a function of drive level and fundamental load impedance is derived. Calculations show that, under appropriate operating conditions, it is sufficient to modulate the transistor load reactance to enable high-efficiency operation (>;70%) over a large output power dynamic range (>;10 dB) with high transistor power utilization. Such dynamic load modulation (DLM) networks are an ideal application of continuously tunable varactor technologies. Multiharmonic load-pull measurements are performed on a GaN HEMT and experimentally verify the theory of operation. A demonstrator amplifier using an SiC varactor technology is then designed and characterized by static measurements. The amplifier has a peak power of 38 dBm at 2.08 GHz and maintains efficiencies above 45% over 8 dB of power dynamic range. An analysis of the load network losses is performed to show the potential of the class-J DLM transmitter concept.