A Cryogenic SiGe BiCMOS Hybrid Class B/C Mode-Switching VCO Achieving 201dBc/Hz Figure-of-Merit and 4.2GHz Frequency Tuning Range.

The interconnects between a quantum processor and control electronics can be made more compact and reliable by placing classical circuits at cryogenic temperature (CT), closer to that of qubits. Low ambient temperature is also favorable to lower the noise of electronics, which is critical for quantum computing applications. Qubit control requires microwave signals modulated by baseband arbitrary waveform envelopes, so as to generate 10ns-to-100ns periodic pulsed signals to manipulate the qubit state [1].In order to prevent qubit state dephasing, the carrier should have a precision better than 1.9kHz (rms). The signal noise bandwidth should be limited from above by the qubit operation speed and from below by the echo-period [1]. To ensure scalability, signal sources should be tunable in a wide range, e.g., 3-to-9GHz for superconducting qubits, assuming enough margin to adapt to PVT variations. To address these constraints, a cryo-CMOS class F 2, 3 LC-tank voltage-controlled oscillator (VCO) was first reported in [1], with a precision of 3.95kHz (rms) at 4.2K and a power consumption of 7-to-19mW with FTR of 5.7-to-7.3 GHz. In [2], a cryo-CMOS 4.4-to-5.3GHz class D/F 2 VCO with an automatic common-mode resonance calibration was presented. Both VCOs suffer from the near-carrier phase noise (PN), i.e., flicker noise region, increasing at CT.Although harmonic-rich tanks have been employed in these designs to suppress flicker noise, the 1/f corners were still easily increased from hundreds of kHz at room temperature (RT) to several MHz at CT. The deterioration of 1/f noise for VCOs can cause difficulties in cryo-CMOS PLL designs for quantum interface applications.