Zero-Power Feed-Forward Spur Cancelation for Supply-Regulated CMOS Ring PLLs

Abstract

A new reference-spur cancelation technique is presented for supply-regulated ring-oscillator-based integer-N phase-locked loops (PLLs). A passive RC filter is used to implement a feed-forward (FF) spur-coupling path to perform spur cancelation at the PLL control signal. The proposed technique achieves a simulated spur cancelation of about 22 dB at the first spur harmonic. The simulated postcancelation spur value is −79 dBc for an oscillator gain of 0.1 GHz/V and −46 dBc for an oscillator gain of 6 GHz/V. Spur cancelation is also robust against large process, voltage, and temperature variations in the gain and bandwidth of the FF path. A 1-GHz integer-N PLL prototype in a 65-nm CMOS process has a measured cancelation of 19.5 and 13 dB at the first and the second spur harmonic, respectively, with $320~\mu \text{W}$ of total power consumption. The PLL prototype has an oscillator gain of 1.5 GHz/V, which results in a postcancelation spur of −53 dBc. The proposed zero-power technique is suitable for low-power PLLs as it achieves a large spur cancelation without requiring any additional power consumption or calibration.