Study On GaAs PHEMT Nonlinear Model And Millimeter Monolithic Power Amplifier

The high-speed development of microelectronics technology and military demands are the main strength to drive microwave monolithic integrated circuits forward. The MMICs can be applied to guidance, radar and satellite communications, and so on. The MMICs become more and more important in national economic construction and the building of national defence. The appearance of heterojunction high electron mobility devices has made the new vigor poured into the development of GaAs MMICs. Pseudomorphic high electron mobility transistors (PHEMTs) have outstanding high-frequency characteristics, power characteristics and low-noise characteristics. And these merits have made the PHEMTs one of the most promising devices. The large-signal nonlinear equivalent-circuit model of PHEMTs has played the key role in MMICs designs, and the model is the bridge between the circuit design and processing design. It is able to improve the circuit design accuracy, decrease the processing repeating, reduce the production cost and shorten research period. The emphasis of this work lies in the study of GaAs PHEMT nonlinear model and the design of millimeter-wave monolithic power amplifier. Detailed study contents are as follows:1. The equivalent circuit models of the primary passive elements in MMICs (including square spiral inductors and MIM capacitors) have been deeply studied. In addition, physical analytical expressions have been given in detail. Furthermore, new formulas taking account of the frequency effect on the self-inductance and feedback capacitance in a spiral inductor equivalent-circuit model are proposed.2. From the physical structure and specific process, the nonlinear equivalent-circuit models of the PHEMT devices have been established. The current models (including the drain current model and the gate current model which is able to reflect the forward characteristics), and the nonlinear capacitance model have been studied deeply. Based on the measured data, the extraction method of the extrinsic and intrinsic parts of the equivalent circuit model has been expatiated. Modified current model equations have been developed to more accurately simulate the current-voltage characteristics of GaAs PHEMTs over a wide range of temperature. And the modified model has been integrated into the ADS symbolically defined device to simulate the PHEMTs' microwave characteristics. The verification results have shown that the proposed nonlinear equivalent circuit model can accurately predict the small-signal S-parameters and the current-voltage characteristics.3. To verify the accuracy of the extraction approach of the nonlinear model in this work, Ka-band monolithic power amplifiers have been designed and fabricated. Good agreement between the simulated and measured data is obtained. Also, the effect of key parts of the PA on the whole circuit performance has been studied and analyzed. As the experimental results shown, the nonlinear equivalent-circuit models and the proposed extraction approach are feasible and accurate.4. The general concept and operators of genetic algorithm (GA) have been illustrated in detail. And the GA has successfully been utilized in the parameters extraction of nonlinear equivalent circuits. An interface program has been developed by author independently, HFSS,ADS and GA have been integrated into this software. The function of HFSS and ADS design softwares has been extended greatly. The validity of GA has been verified by two examples of microstrip-to-waveguide transition structures.