Design of an Operational Amplifier with Depletion-Mode Transistors Only in Monolithic GaN Technology

This thesis presents the design and analysis of an operational amplifier fully implemented in GaN technology, with the aim of exploring the feasibility and benefits of integrating analog building blocks directly on wide bandgap devices. Starting from a conventional Si BCD implementation, used as a reference baseline due to its predictability and extensive presence in literature, the work transitions to a GaN-only realization, addressing the challenges posed by the absence of PMOS devices and conventional diodes in monolithic GaN processes. A systematic comparison between enhancement-mode and depletion-mode GaN transistors was performed, highlighting the superior characteristics of depletion-mode devices in terms of transconductance, output resistance, and noise performance. These results, supported by both simulations and literature, motivated the choice of depletion-mode GaN as the foundation for all basic analog building blocks, including current sources, current mirrors, and diode equivalents. The proposed amplifier adopts a folded cascode topology with a second gain stage and a source follower output, optimized to operate with NMOS only devices. Alternative implementations of key biasing elements were in vestigated to replace unavailable components, ensuring functionality with out sacrificing stability or performance. The study confirms the potential of GaN technology for the integration of analog circuits in high-frequency power systems, where reduced parasitics, higher efficiency, and compact integration are critical. At the same time, it outlines the limitations and design constraints inherent to current GaN processes, paving the way for future developments in monolithic integration of analog and power electronics.