Cejun Wei

Analysis and experimental waveform study on inverse class class-F mode of microwave power FETs

The new inverse class F operation mode for high-efficiency power amplifiers is analyzed. Unlike regular class F, it requires an open circuit termination at the second harmonic and a small impedance termination at the third harmonic. The inverse class F features higher PAE than class F but requires transistors with higher breakdown voltages. A study performed using the waveform measurement technique in conjunction with the active/passive load-pull system showed PAE=83% for the inverse class F compared to PAE=64% for the class F. The measured results are in good agreement with the analytical prediction.

Improved breakdown voltage and hot-electron reliability PHEMT for high efficiency power amplifiers

By increasing the first recess width on the drain side of the gate, PHEMT breakdown was increased by as much as 5 V and hot electron RF stress was reduced by a factor of 2.5 to 3.5 with minor change in saturated power and power-added efficiency. Pulsed IV, loadpull and reliability measurement results are presented for PHEMT devices with various recess structures. The wide recess PHEMT provides necessary reliability margin for high efficiency and high mismatch operation of power amplifiers.

Four terminal GaAs-InGaP BIFET DC model for wireless application

Recently BIFET, a four-terminal MESFET with a p-layer as backgate, emerged as a new technology for wireless, application, that allows HBT and FET to integrate onto same wafer and therefore expands functionalities of circuits and reduce the cost. A novel four-terminal DC model was developed for the first time for accurate DC applications. In this model, the drain current, gate current as well as leakage current are 3D functions that model accurately all terminal currents as well as temperature dependence. The model also predicts very well IV curves for the case when backgate is connected to source or to gate and therefore the device reduces to three-terminal. The model has been used in SKYWORKS for complex PA module design that found applications for wireless communications.

Alpha owned PHEMT model and its verification by load-pull and waveform measurements

Alpha-owned PHEMT model (AOPM) is presented which takes into account high-order derivative fitting in I-V curves, charge-conservation, dispersion/self-heating, and gate current caused by different mechanisms. In order to assess the accuracy of the model, verification has been performed based on complex fundamental and harmonic load-pull behaviour and the device voltage and current waveform. The simulated results are in excellent agreement with the measured data. It is, therefore, important to satisfy all the discussed useful criteria in building an accurate device model to predict adequate power performance for optimum power amplifier design.

Electromagnetic only HEMT model for switch design

Electromagnetic (EM) only HEMT model has been proposed and realized with commercial available EM simulator. EM analysis has been applied, for the first time, to the intrinsic part of HEMT device. The small signal behaviors of HEMT can be accurately predicted based directly on the layout and process information. After introducing two EM HEMT models for HEMTs in both on and off states, entire switch circuit, as a whole, can be EM simulated. The prediction accuracy for switch performance can be remarkably improved by taking into account all of the distributed and coupling effects inside the circuit.

Large-signal PHEMT switch model, which accurately predicts harmonics and two-tone inter-modulation distortion

In this paper, we present a comprehensive large-signal PHEMT switch model and address critical switch modeling issues. Reciprocity, dispersion, leakages, and sub-pinchoff, and charge conservation all play important role in generating a realistic large-signal switch model. Device nonlinearities covering linear, saturation, sub-pinchoff and deep pinchoff regions are taken into account in the model. The model has been verified by comparing simulated dc characteristics, S-parameters and power harmonics performance of switch devices with measured results. The model also successfully predicts harmonics, two-tone IP3 and cross-modulation in various switch circuits.

Multi-Gate pHEMT Modeling for Switch Applications

Multi-gate pHEMTs are extensively used in pHEMT switch circuits for wireless communication applications due to their size advantage. The intuitive modeling approach which considers a multiple-gate pHEMT to be a stack of single-gate FETs is far from adequate. Crucial factors in multi-gate pHEMT modeling include accurate leakage, CV below pinch-off, surface traps effects, and distribution features for large size switch FETs. In this paper we will address certain techniques to model both intrinsic FETs and extrinsic parasitic components. Our multi-gate pHEMT model was verified by comparisons of a variety of performances between modeled and measured data, including leakages, floating voltages, and CV curves on device level. In a switch application, comparisons of harmonics as a function of frequency at high driving power for both GSM and DCS bands show excellent agreement between model prediction and measured data as well.

Novel approach to a consistent large-signal and small-signal modeling of power PHEMTs

A new method is presented to address the Gm and Gds dispersion in large-signal power PHEMT modeling. Instead of using a single DC current source or two current sources for DC and RF respectively, three 4-D sources as functions of Vdo, Vgo, Vgs, and Vds, are introduced to model DC current, RF Gm and RF Gds independently. A model constructed based on the new approach shows consistency in predicting large-signal performance and small-signal S-parameter response over a wide bias range. The model is verified by comparing the modeled DC, RF Gm and RF Gds, bias-dependent S-parameter, power performance as well as device port waveforms at power driving condition.

Temperature dependent linear HEMT model extracted with multi-temperature optimization

Temperature dependent model is conventionally developed with 1) individual linear model extraction at each temperature and 2) temperature dependence extraction for each model parameter. A novel approach based on a multi-temperature optimization is proposed in this study. The new approach is faster and more accurate since the linear models at different temperatures are extracted simultaneously and inter-relatedly. It has been found, based on the model extracted, that there is a specific gate-source voltage of Vgs0, where the transconductance (Gm) keeps constant versus temperature. Gm increases (decreases) with temperature for Vgs<;Vgs0 (Vgs>;Vgs0). With increasing temperature, a substantial decrease in extrinsic inductance is also observed. Our findings are believed to be useful for designing HEMT amplifiers with less temperature dependence.

A comprehensive PHEMT core model for switch applications

A comprehensive non-linear PHEMT core model for switch applications is described. The model combines an accurate description of CV below pinch-off and a 2D CV function above pinch-off for better charge and capacitance modeling. At the same time, more accurate is the models IV prediction on the current in the near pinch-off region. The model has detailed leakage equations and dispersion function covering a wide range of operation, and taking gate lag into consideration. The model was verified by a variety of measured data, including IV/transfer curves, leakages, floating voltages and S-parameters/CV curves. In a switch application, comparison between modeled and measured data on harmonics, insertion loss and isolation regarding various driving power shows excellent and consistent agreement in both on-state and off-state.