Broadband GaN MMIC Power Amplifiers design

Abstract

Monolithic microwave integrated circuits (MMIC) based on gallium nitride (GaN) high electron mobility transistors (HEMT) have the advantage of providing broadband power performance (Milligan et al., 2007). The high breakdown voltage and high current density of GaN devices provide higher power density than the traditional technology based on GaAs. This allows the use of smaller devices for the same output power, and since impedance is higher for smaller devices, broadband matching becomes easier. In this chapter, we summarise the design procedure of broadband MMIC high power amplifiers (HPA). Although the strategy is quite similar for most semiconductors used in HPAs, some special considerations, as well as, experimental results will be focused on GaN technology. Apart from design considerations to achieve the desired RF response, it is essential to analyse the stability of the designed HPA to guarantee that no oscillation phenomena arises. In first place, the transistors are analysed using Rollet's linear K factor. Next, it is also critical to perform nonlinear parametric and odd stability studies under high power excitation. The strategy adopted for this analysis is based on pole-zero identification of the frequency response obtained at critical nodes of the final circuit (Barquinero et al., 2007). Finally, to avoid irreversible device degradation, thermal simulations are required to accurately predict the highest channel temperature and thermal coupling between transistors.