Kelvin Yuk

A Wideband Multiharmonic Empirical Large-Signal Model for High-Power GaN HEMTs With Self-Heating and Charge-Trapping Effects

A complete empirical large-signal model for high-power AlGaN/GaN HEMTs (GaN HEMT) utilizing an improved drain current (Ids) formulation with self-heating and charge- trapping modifications is presented. The new drain current equation accurately models the asymmetric bell-shaped transconductance (gm) for high Ids over a large range of biases. A method of systematically employing dynamic IV behavior using pulsed-gate IV and pulsed-gate-pulsed-drain IV datasets over a wide variety of thermal and charge-trapping conditions is presented. The composite nonlinear model accurately predicts the dynamic IV behavior, S-parameters up to 10 GHz, and large-signal wideband harmonic behavior for a multitude of quiescent gate-source and drain-source biases as well as third-order intermodulation distortion (IM3).

An Empirical Large-Signal Model for SiC MESFETs With Self-Heating Thermal Model

An empirical large-signal model for high-power microwave silicon-carbide MESFETs capable of predicting self-heating thermal behavior is presented. A generalized drain-current equation based on pulsed-gate IV characteristics measuring up to 2 A and 58 V is presented along with its dependence on temperature. A thermal subcircuit with a nonlinear thermal resistance characterized by a dc method is used to model the temperature behavior of the device. The effect of substrate trapping is modeled as a gate-source voltage correction. The complete drain-current model accurately predicts pulsed-gate and pulsed-gate-and-drain IV characteristics for various quiescent biases, as well as static IV characteristics. The complete large-signal model is shown to accurately predict S -parameters, large-signal output, and input reflected power across biases and frequencies, and third-order intermodulation products.

Advances in active microwave frequency multipliers

Microwave frequency multipliers provide a high performance means of generating microwave and millimeter-wave signals in a wide variety of communications and radar systems. The advances in active microwave frequency multipliers due to improvements in technology and design are significant in providing increased conversion gain, efficiency and frequency output. This work overviews the applications, topologies and performance of state-of-the-art active frequency multipliers. Some new circuit techniques are identified.

High power, high conversion gain frequency doublers using SiC MESFETs and AlGaN/GaN HEMTs

High power, high conversion gain microwave frequency doublers using wide bandgap semiconductor devices are developed. A method of determining the optimal harmonic terminations using accurate nonlinear computer models and load- and source-pull simulations is described. Synthesis of these impedances using matching and reflector networks have produced doublers with increased output power, conversion gain and very high suppression of the first and third harmonics. A SiC MESFET-based frequency doubler at fo=2.00GHz producing up to 10.00dB conversion gain and 6.31 Watts 2fo output power is presented. An AlGaN/GaN HEMT-based frequency doubler at fo=3.33GHz producing up to 14.80dB conversion gain and 4.14W 2fo output power is also presented. The second harmonic power measurements confirm the accurate predictions made by the nonlinear model.

An improved empirical large-signal model for high-power GaN HEMTs including self-heating and charge-trapping effects

A new empirical large-signal model for high-power GaN HEMTs utilizing an improved drain current (Ids) model is presented. The new Ids formulation accurately predicts the asymmetric bell-shaped transconductance (gm) over a large drain-source bias range which is crucial in modeling high-power GaN HEMTs. A method of utilizing a combination of pulsed-gate (PGIV) and pulsed-gate-and-drain (PIV) IV measurements to characterize the dispersive behavior of GaN HEMT nonlinear Ids characteristics is developed. Dispersion due to self heating is modeled by modifying Ids parameters as a function of the temperature change and drain-source bias. Dispersion due to trapping is modeled using an effective gate-source voltage model. Accurate predictions of the RF small-signal and large-signal performance are demonstrated for two quiescent biases.

A simplified, empirical large-signal model for SiC MESFETs

A new, simplified empirical large-signal model for high power microwave SiC MESFFTs is presented. A generalized drain current source equation is developed, allowing close predictions of both pulsed and static IV characteristics, which vary significantly due to current dispersion. Thv drain current source is based on pulsed IV measurements and accurately predicts the gm and gds without supplemental RF current source generators as typically used in other models. The model is shown to accurately predict the output and input reflected power over an available power range of +10dBm to +36dBm for three harmonics while maintaining the ability to compute the small-signal S-parameters.

Design of a high power, wideband power amplifier using AlGaN/GaN HEMT

A wideband Gallium Nitride (GaN) HEMT power amplifier (PA) achieving 7.6W output power over 1.1 GHz bandwidth at fo = 2.75 GHz is presented. A systematic design and synthesis of wideband low-pass matching networks realizing optimal fundamental impedance is applied. These techniques have produced amplifiers with increased output power, efficiency and very large fractional bandwidth. Additionally, the PA can achieve a maximum 61% power added efficiency. This work seeks to maximize the usable bandwidth of the GaN HEMT PA to the maximum possible operating frequency.

Future directions for GaN in 5G and satellite communications

GaN will play a strong role in advanced RF and microwave applications including 5G and satellite communications. The specifications of these systems will push next-gen GaN devices towards mm-wave operation. The challenges and opportunities for commercial deployment of GaN are identified and a variety of circuit designs are presented. A 5G high-linearity power amplifier MMIC in 0.20um GaN with Pout=36dBm at 51.1% PAE and a Sat-com Ku-band mixer in 0.25um GaN with conversion loss < 10.5dB and IIP3=36.4dBm are demonstrated.