An X-band ultra-low phase noise differential Colpitts voltage-controlled oscillator using 0.15 μm pseudomorphic high electron mobility transistor technology

A low phase noise and a high output power X-band differential Colpitts pseudomorphic high electron mobility transistor (pHEMT) voltage-controlled oscillator (VCO) is proposed in this study. In general, pHEMT achieves a lower noise up-conversion factor than heterojunction bipolar transistor because of the inherent linear behaviour at optimal gate bias voltage. Therefore, a high linearity 0.15 μm gate length power pHEMT with Colpitts architecture was beneficial for obtaining a low phase noise oscillator together with a high output power characteristic. It achieves an excellent figure of merit of −181.6 dBc/Hz and a power output of 0.67 dBm at 8.6 GHz. In this design, depletion-mode pHEMT was adopted in the VCO core, and a balanced structure was chosen for Colpitts topology to suppress undesired common-mode noise. The VCO was operated from 8.5 GHz to 9.35 GHz with 9.4% tuning range; the measured phase noises at 1 MHz offset were −105.6 dBc/Hz at 9 GHz and −120.46 dBc/Hz at 8.6 GHz, respectively. The current ...