A 951-fsrms Period Jitter 3.2% Modulation Range in-Band Modulation Spread-Spectrum Clock Generator

Abstract

A spread-spectrum clock generator is proposed based on an in-band phase modulation. In a charge-pump phase-locked loop configuration, the input phase modulation signal is applied to the proposed charge-based discrete-time loop filter. The phase difference between the input phase modulation signal and the output clock feedback phase is sampled and applied to the control voltage of an oscillator. The loop gain of the clock generator pushes the output clock phase to accurately trace the input phase modulation signal. This article achieves 3.2% spread-spectrum modulation range and 26.51-dB spread-spectrum attenuation at 352-MHz output frequency using a 2-MHz reference frequency. The in-band modulation improves a design sensitivity, and a 298-ppm modulation range error is measured with over 140% $K_{\mathrm{ VCO}}$ perturbations. This spread-spectrum clock generator is implemented in a 0.18- $\mu \text{m}$ CMOS, and achieves 951-fsrms period jitter while consuming 9.98 mW from a 1.8-V power supply.