A 208-MHz, 0.75-mW Self-Calibrated Reference Frequency Quadrupler for a 2-GHz Fractional-N Ring-PLL in 4nm FinFET CMOS

This paper presents a 208-MHz, 0.75-mW selfcalibrated reference frequency quadrupler (RFQ), which provides a 4x higher reference clock with minimal deterministic frequency error. The digital-assisted calibration technique is exploited to compensate wide range of frequency and duty cycle errors and to reduce the noise degradation of analog calibration loop. Also, instead of utilizing a duty cycle corrector for 2x clock, reusing a delay cell reduces the power consumption by 50%. The fractional-N ring-PLL with the proposed RFQ was implemented in a 4nm FinFET CMOS process. The active area of the RFQ is 0.0175mm2 while the whole PLL occupies the area of 0.109mm2. By using the RFQ, the measured RMS-jitter of the PLL is definitely improved from 6.6ps to 3.35ps at 1.92GHz output frequency.