High-resolution 60-GHz DCOs with reconfigurable distributed metal capacitors in passive resonators

Mm-wave digitally-controlled oscillators (DCOs) with reconfigurable passive resonators are proposed, which achieve wide tuning range (>;10%) and fine frequency resolution (<;1 MHz) simultaneously. Two 60-GHz implementations: a fine-resolution inductor-based DCO (L-DCO) and a transformer-based DCO (T-DCO) are demonstrated in 90-nm CMOS, exploiting metal capacitors only for frequency tuning. Both DCOs obtain >;9.7% linear tuning range and phase noise lower than -90.5 dBc/Hz at 1-MHz offset across the 56-62 GHz range. The T-DCO achieves fine frequency tuning step of 2.5 MHz, whereas that of the L-DCO is better than 160 kHz. The L-DCO and T-DCO consume 10 mA and 12 mA, respectively, from a 1.2-V supply. The core size of each DCO is 0.4×0.4 mm².