A Dual-Loop Spread-Spectrum Clock Generator with Accurate Spread Ratio

This paper presents a spread-spectrum clock generator (SSCG) based on voltage-controlled oscillator (VCO) direct modulation. An auxiliary frequency-locked loop has been employed to guarantee a stable and accurate spread ratio under the variations of process, voltage and temperature (PVT). Besides, the spread ratio can be programmed via different counting value in the auxiliary loop. Implemented in UMC 0.18-μm CMOS technology, the SSCG achieves a 9.97 dB reduction in the peak power spectrum with 0.5% spreading at 31.56 kHz modulation frequency. The die area of the SSCG is 0.42×0.45mm
²
.