A GaAs Colpitts VCO Using g_m-Boosting and Collector-Emitter Cross-Coupling Techniques

A GaAs Colpitts voltage controlled oscillator with low phase noise is presented in this brief. Firstly, the g _m -boosting technique realized by an inductor located at the emitter of heterojunction bipolar transistor is applied to relax the oscillation start-up requirements and speed up the oscillation. Moreover, a Collector-Emitter cross-coupling capacitor is adopted to improve the loaded quality factor and oscillation amplitude of the tank by reducing the transformer ratio, which improves the phase noise in turn. Finally, in proof of the concept, a voltage controlled oscillator prototype is fabricated and designed in 2-μm GaAs HBT process. The measured results demonstrate a phase noise of -137.44 dBc/Hz at 1MHz offset with figure of merit of -192dBc/Hz and a tuning frequency bandwidth from 3.25 to 3.4GHz. Compared with the conventional Colpitts voltage controlled oscillator, the phase noise of the proposed voltage controlled oscillator with g _m -boosting and Collector- Emitter cross-coupling techniques has been improved 6.67 dB.