Design of a X-band GaN oscillator: from the low frequency noise device characterization and large signal modeling to circuit design

Although GaN technologies were initially developed for solid state source amplifiers, it was recently demonstrated that AlGaN/GaN HEMT transistors were also suitable for low noise applications such as LNA (Tartarin et al., 2005). The frequency synthesis is not yet widely explored for these technologies. In this paper the design of a low phase noise X-band oscillator is proposed. The low frequency noise performance and the residual phase noise, as well as dynamic S-parameters were carried out on AlGaN/GaN HEMT grown on SiC. A large-signal modeling technique is also presented. The reduced complexity and the good accuracy of our large signal model permits an efficient circuit design, without intensive knowledge of the technological device parameters. These characterization and modeling tools are used for the design of an 1-stage oscillator working at 10 GHz delivering 20dBm

I. Introduction

AlGaN/GaN field effect transistor offers excellent potential for microwave applications. The high band-gap of GaN (3.4eV) gives to AlGaN/GaN devices a high robustness against external RF aggressions, thanks to their high breakdown voltage and good thermal conductivity. Moreover, high microwave output power levels are useful to reduce the PA'sdesign complexity, while these devices also take benefit from low noise figures at high frequency for LNA's design. This high power levels handling can also avoid the integration of any amplification buffer at the oscillator output to optimize the mixer compression gain. Moreover the devices good layer quality was reported in numerous papers thanks to low frequency noise (LFN) characterization. Therefore these devices can be used to design low phase noise non-linear circuits such as oscillators.