A Low-Reference-Spur Injection-Locked Clock Multiplier Using Sub-Sampling Frequency Tracking Loop and Injection Pulse Timing Calibrator

Abstract

This article presents an injection-locked clock multiplier (ILCM) achieving the low-reference spur (spurREF) with minimal overhead of a calibrator. To remove the dominant sources of frequency error, which are frequency drift (fDF), phase offset (ΦOS), and injection-induced phase error (ΦINJ), the ILCM employs a compact and power-efficient calibrator that combines a sub-sampling frequency tracking loop (SSFTL) and an injection pulse timing calibrator (IPTC). The proposed calibrator eliminates ΦINJ by adjusting the injection timing, simultaneously removing fDF and ΦOS. Furthermore, by leveraging the same signal for both injection and sampling, the proposed ILCM suppresses sampling-induced frequency modulation without requiring an isolation buffer and additional calibration circuit. Fabricated in a 28-nm CMOS, the ILCM achieves a spurREF of −81.36 dBc and an rms jitter of 280.9 fs at a 2.1-GHz output frequency.