Integrated VCOs in Gallium Arsenide HEMT technologies with a novel varactor structure

Licentiate thesis, 2006

This thesis presents results on metamorphic and pseudomorpic GaAs HEMT based Voltage Controlled Oscillators and a novel high-Q varactor structure, used in the VCOs, together with a straightforward extraction procedure for the varactors. Theory and fundamentals around LC-oscillators with oscillator criteria, phase noise and different topologies are given as background together with VCO phase noise measurement methods and an overview on device flicker noise; its physical origin and measurement. Furthermore, design guidelines and suggestions for successful integrated VCO design is presented using a 7 GHz mHEMT VCO as example. It is also shown that the flicker noise generation in mHEMT and pHEMT increases rapidly with drain source voltage leading to a changed optimal Vds bias in the VCO compared to if these noise sources were non existent. Finally, the conclusion is made that a mHEMT process is equally suitable for VCOs as a pHEMT process with the mHEMT version more favorable from a power consumption perspective.