A Wide-Tuning-Range Low-Phase-Noise mm-Wave CMOS VCO With Switchable Transformer-Based Tank

In this letter, we present a millimeter-wave (mm-wave) complementary metal-oxide semiconductor (CMOS) voltage-controlled oscillator (VCO) that has a wide frequency tuning range (TR) and low phase noise (PN). The proposed architecture benefits from a switchable transformer-based
LC
-tank which significantly improves the TR without compromising the PN performance. The proposed 3-D transformer consists of three mutually coupled, switched spiral coils. The secondary and tertiary spiral coils are switched in or out of the circuit and depending on the switch states, the proposed VCO achieves four overlapping frequency sub-bands and a wide overall TR. To lower the loading effect of the switches, we present a design guideline which is based on the mutual coupling between the auxiliary coils. As a proof-of-concept, a mm-wave VCO is implemented in a 65-nm CMOS process. Based on the measurement results, the VCO achieves an average PN of −111.9 dBc/Hz at 10 MHz offset over the entire frequency TR, and a TR of ~18%, from 50.1 to 59.8 GHz, resulting in a figure-of-merit (FOM) incorporating the TR (FOM
_T
) of −184 dBc/Hz. The VCO core consumes 6.2 mW from a 1-V supply and excluding the pads occupies a compact silicon area of 0.06 mm
²
.