Design and Analysis of Low-Power High-Frequency Robust Sub-Harmonic Injection-Locked Clock Multipliers

Abstract

A low-jitter, low-power LC-based injection-locked clock multiplier (ILCM) with a digital frequency-tracking loop (FTL) is presented. Based on a pulse gating technique, the proposed FTL continuously tunes the oscillator's free-running frequency to ensure robust operation across PVT variations. The FTL resolves the race condition existing in injection-locked PLLs by decoupling frequency tuning from the injection path, such that the phase-locking condition is only determined by the injection path. This paper also introduces an accurate theoretical large-signal analysis for phase domain response (PDR) of injection-locked oscillators (ILOs). The proposed PDR analysis captures the asymmetric nature of ILO's lock-in range, and the impact of frequency error on injection strength and phase noise performance. The proposed architecture and analysis are demonstrated by a prototype fabricated in 65 nm CMOS process with active area of 0.25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The prototype ILCM generates output clock in the range of 6.75-8.25 GHz by multiplying the reference clock by 64. It achieves superior integrated jitter performance of 190 f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">srms</sub> , while consuming 2.25 mW power. This translates to an excellent figure-of-merit (FoM) of -251 dB, which is the best reported high-frequency clock multiplier.