Design of a 24-GHz VCO using magnetic coupling of gate-drain through a transformer

In this work, we propose a 24-GHz VCO using a transformer. In the mm-wave band, parasitic components of the passive device and feeding line degrade VCO performance. To reduce the undesired effects of passive devices, we replaced the transformer instead of passive devices such as the inductor or capacitor. In addition, we propose a frequency tuning technique using a gate bias instead of a typical varactor. To verify the feasibility of the proposed structure, we designed the VCO using a 110-nm RFCMOS process. The measured frequency tuning range of VCO was 22.7 to 24.2 GHz, and it had output power of 8.4 dBm at 24 GHz. The measured phase noise was -95.33 dBc/Hz at 1 MHz, offset at an operating frequency of 23.6 GHz. The chip size was 370 × 380 μm², including test pads.