60GHz VCOs with transmission line resonator in a 0.25μm SiGe BiCMOS technology

In this paper, two 60 GHz LC-VCOs are compared. The varactorless oscillators are identical except for the implementation of the inductors. One oscillator uses a traditional spiral inductor, the other oscillator uses a shorted transmission line as inductor. Although the spiral inductor is favorable in terms of quality factor and self-resonant frequency, the shorted transmission line offers superior isolation from the substrate. The solid ground shield of the transmission line offers reduced sensitivity to substrate interference. The 60 GHz VCO with shorted transmission line as inductor achieves a measured 22.6 dB lower power level of the main oscillator sideband for a given interference level. The experiment is performed in a BiCMOS process, but the results are also applicable to CMOS technologies.