A low phase noise Colpitts VCO for Ku-band applications

A 12.74 GHz low phase noise Colpitts VCO has been designed and fabricated in a 0.25μm SiGe:C BiCMOS technology. The balanced VCO uses a transformer coupled tank and two additional inductors to reduce the current in the feedback loop. The efficiency of energy transfer from active devices to the tank has been improved by these two methods, which leads to a larger output swing for the same DC current. Measured phase noise is better than -100dBc /Hz at 100 kHz offset over the tuning range from 12.43 to 13.08GHz.