Phase-noise improvement of GaAs pHEMT K-band voltage controlled oscillator using tunable field-plate voltage technology

This paper presents a voltage-controlled oscillator (VCO) with low phase noise performance by applying tunable field-plate (FP) voltage on 0.15 ¿m gate length GaAs pseudomorphic high electron mobility transistors (pHEMTs). In this study, the FP metal between gate and drain terminals was connected to a single pad and was controlled by an extra voltage supplier (V_FP). Owing to the depth modulation of field-plate induced depletion region at various field-plate voltages, the device flicker noise were also improved by applying negative VFP. This technique is easy to apply, based on standard pHEMT fabrication, and especially attractive for reducing the phase noise of VCO design without extra power consumption. A tunable phase noise inductor-capacitor (L-C) feedback 21 GHz VCO was fabricated in a standard 0.15 ¿m GaAs pHEMT process. The measured phase-noise of this novel design is -95 dBc/Hz at an offset frequency of 1 MHz and this value can be improved to -99.6 dBc/Hz at VFP of -5.5 V. The core dc power consumption of this circuit is 30.8 mW.