Robust Design Approach Towards GaN HEMT RF Front End Amplifier for High Power Transceivers

Abstract

This research work focuses on the design and implementation of Gallium Nitride High Electron Mobility Transistor (GaN HEMT) based Microwave Low Noise Amplifiers (LNAs) and Power Amplifiers (PAs) with novel techniques for modern wireless broadband and dual-band communications. The Low Noise Amplifiers account for the majority of the system’s Noise Figure, while Power Amplifiers account for most of the high output power. As a result, front-end designs are being researched to improve the device’s signal to noise ratio (SNR) with highly linear output power. The primary objective of the proposed front-end is to produce low NF, small and large signal flat gain, excellent linearity, high efficiency, and high i/o power while minimum power consumption at the ultra-high frequency to microwave bands of operation. Firstly, a performance analysis of the GaN HEMT based low noise amplifier (LNA) using even-odd mode matching techniques has been developed. The proposed GaN LNA circuit provides a high input/output (i/o) power, and ultra-low noise over wideband ranging from 0.5 to 2.7 GHz with fractional impedance bandwidth of 138%. The proposed LNA circuit with the incorporation of input/output broadband stages relaxes 50Ω matching constraints and achieves high input and output power with good stability. The proposed LNA achieves a simulated/measured gain of 16dB/17dB. An ultra-low noise figure of 0.6 dB flat is achieved over a wideband. In addition, the high output power is achieved at 40dBm while input power is 25dBm. The fabricated GaN HEMT LNA circuit has consumed power of 120 mW. The area of the fabricated RF GaN HEMT LNA is 32 × 26 mm2 . Secondly, a GaN HEMT device to circuit approach towards LNA using defective ground bias (DGB) technique has been developed. This is the first MMIC GaN HEMT LNA design to offer dual-bands of operation in both L and S-bands to the author’s best knowledge. The proposed 0.15-μm GaN HEMT device is fabricated using slot radiation phenomenon, which achieved a high output power of 20W. To achieve an optimal noise, high i/o power, and almost flat gain at both L and S-band, the defective ground structure of bias topologies is modelled and optimized. An artificial ground defect is created to offer resonant properties, which utilizes frequency-selective properties to improve the performance of the LNA circuit. The dedicated LNA shows the benefits of compact size, extremely low noise figure of 0.74/1.6 dB, and high output power of 44 dBm. The compact GaN HEMT LNA could overcome the weak signal strength received by RF receivers for modern wireless communication systems. Thirdly, a high efficiency Rat-Race coupler (RRC) based compact GaN HEMT PA design over broadband has been developed. The RRC integrated PA design is proposed for the first time as per author best knowledge. The design methodology used a higher order two open stubs and a rat-race coupler (RRC) at i/o sections to control harmonics impedances. As a proof of concept, a PA is fabricated using a monolithic microwave integrated circuit (MMIC) with 0.15 μm gallium nitride high electron mobility transistor (GaN HEMT) process. The measured result shows that the designed PA achieves a flat power added efficiency (PAE) of 65% - 74 %, output power (Pout) of 44.8 dBm - 46 dBm, and drain efficiency (DE) of 72% - 85 %, over a record wide frequency of 1.8 GHz - 3.6 GHz, which is the highest one among all reported harmonic tuned PAs. Finally, a highly stable PA with three operating bandwidth points has been presented. A unique multi-harmonics-controlled network with three-paths impedance matching structure and proper bias topologies are combined to achieve excellent performance in terms of operating bandwidth, efficiency, and high i/o power. A buffer stage of impedance matching is generated by proposed three paths to reducing the harmonics, promoting the targeted fundamental bandwidth. To verify the methodology, a wideband PA is implemented with a 25-W wolfspeed Cree model CG2H40025F GaN HEMT device. The implemented PA is simulated and post-simulated, which provide a fractional bandwidth of 67 % over the frequency of 2 to 4 GHz, with DE of 54-65 %, PAE of 47-52 %, saturated output power of 43.1-44.6 dBm, and a gain of 7.1-9.5 dB. The above results show that PA realized by the proposed novel method is suitable for modern wireless applications. All the proposed GaN HEMT LNAs and PAs are fabricated using a MIC/MMIC process under the supply of 28V. The design of experiment (DoE) and statistical analysis are additional novel contributions towards robust proposed front-end amplifiers in this work. DoE is a new analysis technique to find the individual device parameter’s contribution to the final gain, NF, and return loss. Statistical analysis is also performed to find the yield so that the robustness of the proposed designs is satisfied. A novel harmonically controlled impedance matching techniques are used to design and analyze PAs.