Design And Implementation Of X-Band GaN-Based Internally-Matched Power Amplifier

The III-nitride material system,represented by Ga N(Gallium Nitride), fits perfectly in the fabrication of microwave&millimetrewave power device due to its advantage of wide bandgap, high critical breakdown electric field,high electron mobility, good chemical stability which enables its usage in high temperature circumstance.Ga N HEMT based internally-matched microwave power transistors which have the unique characteristics such as high output power, high gain, low loss and small volume, have gradually driven more and more research interest in recent years and replaced the traditional Ga As based internally-matched power transitors. The thesis focuses on the development of X-band Ga N based internally-matched power transitors in the situation mentioned above.Work of this thesis is based on the self-developed Ga N HEMT which is fabricated on Si C substrate and has gate length of 0.4μm and gate width of 12 mm. Detailed work from fabrication and characterization of the device, design of the microwave schematic circuit to assemble and debug of the internally-matched circuit is carried out. Introduction of the extraction methods of 18-element small signal model together with analysis of transimission line theory and power amplifier theory which lay the foundation of interlly-matched circuit design is given at the beginning of the thesis.The circuit is designed with Agilent ADS software, and loadpull simulation is carried out in order to find the optimal matching impedance. With the combination of T-shaped pre-matched network and power divider/combiner, the optimal matching impedance of the die is transformed to standard 50Ω. Circuit parameters such as stability, linearity of gain and power added efficiency are optimized through small signal S parametre simulation, large signal power sweep simulation and frequency response simulation. In the end, the designed schematic is transformed to layout circuit, and the layout is upgraded to fit the circuit parameters with those simulated from the schematic.The matching capacitor together with power divider/combiner is fabricated, and after that the internally-matched circuits are assembled and debugged. The length and number of bonding wires is analysised with HFSS, and the egienmode of the cavity oftesting fixture is also inspected to ensure that there is no oscillation frequency in the desired band.At last the bias network is designed with Agilent ADS.In the end, the offset of the built microwave power measurement system,along with insertion loss of the testing fixture is measured from a set of careful and reasonable calibration procedures. Power measurement of the assembled 12 mm two-way combined internally-matched circuit shows that the output power reaches 44.02 d Bm at 8GHz with power gain greater than 7 d B,and power added efficiency is 34.2%.In the band from 7.8GHz to 8.2GHz, power gain exhibits more than 6.9d B, with a PAE higher than 33%.