A Programmable Spread Spectrum Clock Generation

In this paper, a spread-spectrum clock generator (SSCG) with triangular modulation is presented. The proposed SSCG with a third-order sigma-delta modulator can generate clocks with center spread ratios of 0.25%, 1%, 1.75%, 2.5%, 3.5%, 5% and down spread ratios of 0.5%, 2%, 3.5%, 5%, 7%, 10%. The SSCG is implemented on a chip using SMIC 0.13 um CMOS process. Measurements show that 11.31 dB attenuation of the EMI at 80 MHz with down spread ratio of 10% and 12.98 dB attenuation at 133.3 M with center spread ratio of 5% can be achieved which have a good agreement with the theoretical calculations.