A 31–46 GHz Dual-Core Class-C VCO Using Switchable Transformers in 28-nm CMOS

This letter presents a dual-core, wide-tuning, class-C voltage-controlled oscillator (VCO) operating at millimeter-wave (mm-wave) frequencies. Each core contains a 7-bit switched capacitor array and a switchable transformer to maximize the entire tuning range. The proposed class-C VCO can achieve low phase noise (PN) by using a noise-filtering technique that blocks the second-harmonic current. The two VCO cores can be turned on or off by setting their bias voltages, eliminating the need for switching transistors in the high-frequency signal path. The proposed dual-core class-C VCO was designed and fabricated using 28-nm CMOS technology, with a core area of 0.048 mm2. The average measured PN is −116 dBc/Hz at 10-MHz offset with a carrier of 36.96 GHz. The tuning range is 39%, from 31 to 46 GHz. The VCO consumes a dc power of 6.8 to 9.9 mW, achieving 181.8 dBc/Hz FOM and 193.6 dBc/Hz FOMT, respectively.