Modeling Of AlGaN/GaN HEMt Power Devices And High Effciency Amplifier Design

With the development of wireless communication and radar exploration, modernelectronic equipment requires microwave power transistor with higher and higherfrequency and power density. In comparison with the first and second generationsemiconductor material, wide band gap semiconductor represented by SiC and GaN hasbetter voltage performance, faster electron drift mobility, higher conductivity and betterresistance of radioactive property. So the wide band gap semiconductor is focused onthe research of semiconductor device. Because of better frequency property and higherpower factor, GaN has wider development in the high frequency band and high powerapplication compared with SiC. Now, the manufacturing of GaN power device has madesome progress, but the model is relatively backward. The model of GaN power device isa very important factor in the design of microwave circuit, the applicability andaccuracy of the model has important effect in the design result. Compared withtraditional power device, AlGaN/GaN HEMT has a lot of difference in the channelformation and current density. The current power device model has some error in thecalculation of self-heating effect and nonlinear characteristics, which limits the overalldevelopment of GaN power device. In order to expedite the application of GaN powerdevice, improving the design of circuit, accelerating the development of GaN device,the model of GaN power device is instant needed. In this paper, the factorcharacteristics of AlGaN/GaN power device was analysed, and the research wascentered around on the experience model. The nonlinear equivalent circuit model wasimproved and the approach of establishing table model was broadened. Based on theX-parameters and Volterra series, the method of model was presented. According to theequivalent circuit model, high efficiency amplifier was designed. Following is thespecific research content:1. Equivalent circuit model of AlGaN/GaN HEMT power deviceSince the number of equivalent component is large and the extraction program iscomplex, the method of undetermined coefficients is used in the calculation programwith help of optimization software. The accuracy is improved. According to the curve of I-V, the formulas of nonlinear current and capacitance are improved which can describethe downward of current with the growth of voltage and the influence of the temperature.This description can reflect the effect of self-heating and temperature distribution. Theformulas are used in ADS software and based on which the current characteristics,frequency and output performance are calculated. Compared with measured data, theimproved nonlinear model can improve the accuracy of predication.2. Table model of AlGaN/GaN HEMT power device based on K nearestneighbors algorithmThe “black box” table model of AlGaN/GaN HEMT power device can neglect thestructure and conduct mechanism and use mathematics operation to model and predictpower device which could apply mathematics method adequately and protectintellectual property effectively. However, the model process needs a lot of measureddata and the algorithm code is always complicated. Based on the drain current andS-parameters data this research established table model of nonlinear equivalentcomponent in which the K nearest neighbors algorithm was improved. The model savesmeasured data and simplifies model structure. With help of Taylor series, nonlinearcomponents are extracted. The output performance is predicted and the accuracy isgood.3. Model of AlGaN/GaN HEMT power device based on X-parameters andVolterra seriesX-parameters can describe precisely the correlation coefficient between everyfrequency component in each port of power device. However, it can difficult reflect theperformance of device in time domain. Volterra series can describe the performance ofpower device in both time domain and frequency domain, but the extracting process istoo complex. X-parameters was conjunction with Volterra series in this research. Basedon X-parameters, kernel function of Volterra series was extracted easily with help ofwhich Volterra model can be used to predict the property of device in time domain andfrequency domain. The method which is a new idea for model can save measurementwork and get good accuracy.4. High effective GaN HEMT amplifier design and measurement based onequivalent circuit modelA class AB GaN power amplifier with50W output and a10W output power GaN amplifier were designed based on each equivalent circuit model. In order to quantizationanalysis the efficiency improvement, two LDMOS amplifier with similar output weredesigned and measured. The comparisons between prediction data, GaN amplifiermeasured data and LDMOS amplifier measured result show that the equivalent circuitmodel has a good accuracy and the GaN amplifier has a high efficiency.To sum up, the current formula in the equivalent circuit model presented in thispaper can be used in simulation software easily and has a good accuracy. The methodsof using KNN algorithm in table model and extracting Volterra series by usingX-parameters provide new approaches for device model and broaden the mind of modelwhich may improve the development of device model.