Diseño de circuitos integrados de microondas basados en tecnologías III-V para la reducción de costes y mejora de la eficiencia de las comunicaciones vía satélite

Abstract

The application of III-V technologies in the field of high-frequency communications has grown exponentially over the last twenty years. However, these technologies and especially gallium nitride (GaN) and gallium arsenide (GaAs) processes are typically used for the implementation of active circuits, such as different types of amplifiers. The design of passive circuits in these technologies remains mainly unresearched. Therefore, the main goal of this PhD. dissertation is the analysis of the viability to implement passive mixers in GaN and GaAs processes as a means to reduce the power consumption of the overall systems and to facilitate the integration of complete MMICs in a more direct manner, which could result in a significant area decrease. With this goal in mind, three passive SSB SHP mixers have been designed using GaN on Si, GaAs and GaN on SiC processes. In order to perform a proper comparison, the same architecture was implemented for all three designs, and the same specifications regarding IF, LO and RF frequency and power were followed. Additionally, some techniques were tested to improve the performance of the design and reduce the area occupation of the designed mixers. Mainly, the quasi-lumped stub technique was applied to reduce the overall size of the circuits, and both non-tapered and tapered octagonal inductors were tested to improve the frequency response of certain subcircuits. As a side result of the analysis of the inductors, an inductor model that can accurately predict the inductance and quality factor of square and octagonal inductors (both non-tapered and tapered) has been developed. This model can be applied to obtain a quick estimation of the performance of an inductor without the need of performing its electromagnetic (EM) simulation. This saves the designer time and can be quite useful if there is no EM simulator available and the physical characteristics of the process are known. The model has been verified through comparison of its results with EM simulations and measured inductors, which were manufactured in a GaN on Si commercial process foundry run. In the same run, the GaN on Si SSB SHP mixer was also manufactured and measured. Due to a lack of funding, the GaAs and GaN on SiC mixer designs had to be verified through schematic and EM simulations in order to perform a comparison between all three designs. Additionally, these circuits have been compared to other designs found in the literature. The results of this comparison show that the selected mixer topology could be applied to communication systems as a means to reduce their power consumption, while guaranteeing good image rejection and isolation results. However, their losses need to be carefully considered, since they could impact the overall performance and may need to be compensated using a driver amplifier. The size of the mixers designed using the SSB SHP topology is in line with other solutions. In fact, if the frequency of operation were higher than the Ku band, allowing for the LO harmonics to be more separate than the RF output of the mixers, the area of the mixers designed with these topology would be smaller, and the effect of the LO stubs on the output would be reduced, thus improving the performance of the mixer even further.