An Area-Efficient CMOS Cross-Coupled <i>LC</i> -VCO Using Nested Intertwined Tail Inductors

An area-efficient CMOS cross-coupled LC-VCO, operating from 5.74 GHz to 8.02 GHz and featuring a tail noise filter with two tail inductors integrated inside the main inductor, is presented for the first time. The tail noise filter comprised two nested intertwined tail inductors (NITIs) and a tail capacitor bank, effectively suppressing phase noise (PN) while generating negligible magnetic couplings between the main inductor and the NITIs. The proposed architecture enables area-efficient CMOS cross-coupled design, even with the two NITIs, but has no performance degradation, i.e., it eliminates the additional area for the tail noise filter. Implemented in 28-nm CMOS process, it consumed 11 mA current from 0.73 V power supply. The LC-VCO achieved PN of −116.38 dBc/Hz at 1 MHz offset frequency for an output frequency of 5.747 GHz. 37% and 27% reductions in silicon area were achieved, over the conventional LC-VCO and an LC-VCO using intertwined tail inductors (ITIs), respectively, without compromising on performance. The proposed design has the smallest area among state-of-the-art LC-VCOs that include a tail noise filter along with competitive PN and frequency tuning range (FTR).