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A High Performance Spread Spectrum Clock Generator Using Two-Point Modulation Scheme

A new spread spectrum clock generator (SSCG) using two-point delta-sigma modulation is presented in this paper. Not only the divider is varied, but also the voltage controlled oscillator is modulated. This technique can enhance the modulation bandwidth so that the effect of EMI suppression is improved with lower order ΣΔ modulator and can simultaneously optimize the jitter and the modulation profile. In addition, the method of two-path is applied to the loop filter to reduce the capacitance value such that the total integration can be achieved. The proposed SSCG has been fabricated in a 0.35μm CMOS process. The clock of 400MHz with center spread ratios of 1.25% and 2.5% are verified. The peak EMI reduction is 19.73dB for the case of 2.5%. The size of chip area is 0.90×0.89mm2.