28 GHz VCO Using Magnetically Tuning Trifilar Transformer in Cryogenic CMOS Application

This paper introduces a cryogenic CMOS voltage-controlled oscillator (VCO) to generate the control signal for spintronic qubits in quantum computing applications. The proposed VCO utilizes a magnetically tuning trifilar transformer to achieve large output swing, low phase noise, and low power consumption. The tertiary coil of the trifilar transformer is applied to tune the primary and the secondary resonance frequency simultaneously to suppress the flicker noise up-conversion. In addition, switching the bias voltage of the center tap in the tertiary coil can achieve a wide tuning range. Fabricated in TSMC 40 nm CMOS process, the 28.3-to-31.4 GHz VCO consumes 5.4 mW under 0.6-V supply voltage, and achieves phase noise of –96.8 dBc/Hz at 1-MHz offset at room temperature (300K). When operating at 4K, the VCO operational frequency is slightly higher, from 29.1 GHz to 33.1 GHz, with a power consumption of 5.6 mW.