Linearity enhancement for GaN HEMT amplifier using parallel transistors with independent gate bias control

GaN HEMTs have high output power density and high efficiency over wide bandwidth. But the linearity of GaN HEMT is typically worse than that of a GaAs device. This paper presents a simple methodology to improve the linearity of GaN HEMT. The proposed method is to split the device into multiple sub-cells in parallel with independently controlled gate bias voltages and then power combine the sub-cell outputs. A prototype amplifier using two 1.25 mm devices in parallel is fabricated. The experimental results shows 4 dBc improvement in IMD3 at design frequency of 900 MHz with similar PAE at moderate power levels and 2 dBc improvement at higher power levels with a 5 % increase in PAE. More importantly, this proposed method improves linearity without substantial penalty in output power or efficiency. Further improvement is possible with additional parallel devices. To the authors' knowledge, this paper represents the first demonstration of this technique for linearization of GaN HEMT devices.