Design of Compact Size CMOS VCO Using Dual-Primary Transformer With Dual-Core for Wide Tuning-Range

In this brief, we design a CMOS-based dual-core voltage-controlled oscillator (VCO) to extend the frequency tuning range. To mitigate the increase in integrated circuit area caused by the LC tanks required for dual-core operation, a dual-primary transformer structure is proposed. The proposed transformer consists of two primary windings and one secondary winding. The primary winding corresponding to the core supporting lower frequencies is designed with two turns to secure sufficient inductance. Thanks to the proposed dual-primary transformer, a compact size is achieved despite the dual-core VCO configuration. To validate the effectiveness of the proposed structure, the VCO is fabricated using a 65-nm RFCMOS process. The fabricated VCO core, including the output buffer, occupies an area of $0.39\times 0.11$ mm2. The measured frequency tuning range spans from 17.8 GHz to 26.9 GHz, with phase noise at 1-MHz offset and output power measured to be lower than −89.6 dBc/Hz and higher than −15.3 dBm, respectively.