Gm-boosted balanced Colpitts compared to conventional balanced Colpitts and cross-coupled VCOs in InGaP HBT technology

This paper presents a very compact (800×600μm²) gm-boosted balanced Colpitts VCO in a customized InGaP HBT process. An excellent phase noise of -112 dBc/Hz@100kHz off-set and tuning range over 10% centers around 6GHz carrier is reached. To the authors best knowledge, this is the first ever gm-boosted balanced Colpitts in InGaP HBT. It is validated that the topology may provide enhanced performance compared to both conventional balanced Colpitts and cross-coupled topologies that are also evaluated in this work. The gm-boosted balanced Colpitts is found to be slightly better than the balanced Colpitts and significantly better than the cross-coupled topology. Particularly, the gm-boosted topology benefits from less variation in phase noise and output power over the tuning range. For all three circuits the phase noise is well predicted using an in-house large-signal noise HBT model. The intrinsic device wave-forms are verified with a large-signal vector network analyzer. It is found that the level of phase noise as well as the simulation accuracy is highly correlated to the wave-forms in the VCO.