A dual-Gm start-up boost technique for wide-band BiCMOS LC-VCOs

This paper presents a start-up boost technique dedicated to BiCMOS LC-oscillators. The proposed technique is applied to wide-band LC-VCOs which generally suffer from increased tank losses and require high bias current to ensure start-up and sustainable oscillation. To overcome these limitations, we propose to connect a bipolar transconductance to intermediate levels of the oscillator's tank in order to enhance the global transconductance and boost the start-up while relaxing the total power consumption. The constraints of the auxiliary transconductance use as well as the achieved improvements relative to power saving are discussed in this paper. In addition, an LC-VCO design using the proposed technique in 0.25-μm BiCMOS technology is described. The oscillator covers the frequency range from 4.82 GHz to 9.86 GHz with 68.7% tuningrange. The achieved phase noise at 1-MHz offset varies from -121 dBc/Hz to -116 dBc/Hz, at 5.24 GHz and 8.8 GHz, respectively, with a maximum power consumption of 18.6 mW from 1.2-V DC supply voltage.