A Low-Reference Spur MDLL-Based Clock Multiplier and Derivation of Discrete-Time Noise Transfer Function for Phase Noise Analysis

A multiplying delay-locked loop (MDLL)-based clock multiplier with a two-step phase aligning architecture and a dual-pulse charge-pump (CP) is proposed to reduce the reference spur level. The architecture has a phase-locked loop mode to align the coarse phase and an MDLL mode to obtain a delay-lock. With non-overlap dual phase detector pulses in the MDLL mode, the CP is directly calibrated in the runtime to minimize its phase offset. A discrete-time noise transfer function (NTF) is also derived to estimate the phase noise of multiplying-delay line from that of delay line. The NTF includes aliasing effect and shows better accuracy than the prior voltage controlled oscillator realignment-based approaches. This clock multiplier occupies an active area of 0.047-mm
²
in 40-nm CMOS process. The clock multiplication ratio (N) is an integer value from 8 to 27. With a low-cost 19.2-MHz TCXO reference, 153.6-518.4 MHz clocks were successfully generated, and a phase noise of -124 dBc/Hz at 100-kHz offset from a 518.4-MHz clock, rms jitter of 1.28 ps, and -65.5 dBc reference spur were measured. The power dissipation at 518.4 MHz was 2.6 mW from the 1.8 and 1.1 V supplies.