A Low Phase Noise and Wide Tuning Range Millimeter-Wave VCO Using Switchable Coupled VCO-Cores

Abstract

This work presents a millimeter-wave (mm-wave) dual-mode voltage-controlled oscillator (VCO) topology with switchable coupled VCO-cores for wide frequency tuning range and low phase noise application. By taking advantage of the different parasitic capacitance of cross-coupled pair when the VCO-core operates in ON and OFF states, the dual-mode operation of VCO can be realized, and the oscillations for both modes can be excited at the lower resonant frequency of tank, such that tank Q and phase noise performance could be improved for both modes. Strongly coupled transformer with large coupling coefficient (k) is utilized to increase the oscillation stability at the desired resonant frequency for both modes. The large k transformer will also facilitate the enhancement of tank Q at the lower resonant frequency. Frequency tuning range of the VCO is increased by properly designing the VCO-cores and combining the frequency bands of the two modes. In addition, the cross-coupled pair of VCO-core at OFF state is able to act as high Q active capacitor, which can further increase the tank Q and thus reduce the phase noise. Fabricated in a 0.18 μm BiCMOS process, the VCO exhibits a wide tuning range of 17.2% from 55.7 GHz to 66 GHz, and low phase noise from -87.5 dBc/Hz to -93.5 dBc/Hz at 1 MHz offset over the entire tuning range.