Limits for Low Supply Voltage Operation of a 5 GHz VCO to Drive a 4-Path Mixer

The design and simulation results of a cross-coupled LC VCO in 28 nm FD-SOI for the 4.8 - 5 GHz band are presented. Following a previous work, it is predicted that 0.26 V is the minimum supply voltage of this VCO. It was verified through simulations that the VCO can operate with 0.25 V supply, consuming 90 μW and has a phase noise of -90.2 dBc/Hz at 1 MHz, while complying with the requirements of the following stage. As a consequence of operating at frequencies above the transition frequency of the transistors, the predictions based on the previous study, are less accurate but still provide a good starting point for the design. Moreover, lifting the previous study hypothesis of having an oscillation frequency at least a decade below the transition frequency of the transistors has allowed to further lowering the minimum supply voltage.