Eigo Kuwata

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

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.

C-Ku band 120% relative bandwidth high efficiency high power amplifier using GaN HEMT

This paper reports on a GaN HEMT (Gallium Nitride High Electron Mobility Transistor) HIC (Hybrid Integrated Circuit) high power amplifier, which features high efficiency over C-Ku band 120% relative bandwidth. It was found that the output impedance of a transistor under high efficiency operation can be modeled by parallel circuit of R and C. In the circuit design, BPF (Band Pass Filter) configuration is employed, where parasitic capacitance of the transistor is utilized as a part of BPF matching circuit. Hence broadband matching was successfully obtained. A C-Ku band GaN HEMT HIC amplifier was manufactured and measured at 30V drain voltage. More than 4W output power and 18% PAE (Power Added Efficiency) were obtained over 120% relative bandwidth. This result is state-of-the-art high efficiency for GaN HEMT HIC amplifier with more than 100% relative bandwidth.

GaN X-band 43% internally-matched FET with 60W output power

An X-band high efficiency GaN internally-matched FET has been developed. Asymmetric matching circuit layout is employed to avoid decrease of efficiency caused by impedance mismatch and unbalance power dividing in matching circuits. The designed asymmetric input and output matching circuits have achieved equal dividing characteristics. A power added efficiency (PAE) of 43.4% and an output power of 47.8 dBm (60.3 W) have been achieved with the developed GaN internally-matched FET.

On the large-signal modeling of High Power AlGaN/GaN HEMTs

In this paper are given some recent results on modeling of High Power GaN HEMT devices. The GaN HEMT is very promising for high power application, but we push device to the limits, so many issues are becoming critical. For example, access resistances Rs, Rd in high power GAN HEMT are bias and temperature dependent - their extraction from cold FET measurements can lead to over optimistic prediction for output power. Thermal management, self-heating modeling are another very important issue - they influence reliability, power and PAE. Models without dynamic self-heating are not practical for GaN. The models without breakdown can easily predict world records for PAE, output power/mm etc. Some examples are given using vectorial Large Signal Measurements (LSNA/NVNA) to provide useful, global info about device behavior, influence of traps, knee voltage walkout etc.

Internally matched GaN FET at C-band with 220W output power and 56% power added efficiency

In this paper, a high power and high efficiency fully internally-matched GaN FET operating at C-band is presented. In this work, a C-band GaN amplifier is designed so that 2nd harmonic impedance is tuned to high efficiency and combining loss is maintained minimum. As a result, 224W output power and 56% power added efficiency was successfully obtained, which is the highest efficiency as for over 200W GaN amplifier operating in C-band.

An X-Band 50W-Output/30%-PAE GaN Power Amplifier with Bandwidth/Ripple-Optimized Bandpass Impedance-Matching Networks

An X-band 50 W GaN power amplifier (PA) is presented, mainly focusing on its impedance-matching networks to realize a specified operating bandwidth of 18 %. Bandpass impedance-matching networks (IMNs) with Chebyshev response are adopted in the PA, where a FET and a pre-matching transmission line can be approximately seen as a shunt parallel-resonant circuit. Mismatch-loss ripple of the Chebyshev IMN can be theoretically optimized in terms of Q-factor of the FET and a specified operational bandwidth. The designed PA has achieved an output power of 50 W and a power-added efficiency (PAE) of more than 30 % in the 18 % relative bandwidth.