A $\text{94.4fs}_{rms}$ Cryogenic Sub-Sampling PLL in 4K for Quantum Computing Applications

This paper presents a fractional-N sub-sampling PLL (SSPLL) for cryogenic frequency source of in the quantum meas-urement and controller system. The proposed SSPLL adopts a 5-bit vector modulator (VM) based phase-interpolator (PI) and a 5-bit digital-to-time converter (DTC) for in-band phase noise sup-pression. According to the measured result, the SSPLL spans from 11.4GHz to 13.8GHz in 4K. When the SSPLL is divided by two, the output frequency is 6.3GHz. The measured RMS jitter is 94.37fs, the phase noise is -113.72dBc/Hz@100kHz, and the figure-of-the-merit (FoM) of -245.9dB is achieved.