A fully integrated spread spectrum clock generator using two-point delta-sigma modulation

Abstract

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. 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 SSG has been fabricated in a 0.35um CMOS process. The clock of 400MHz with center spread ratios of 1.25% and 2.5% are verified. The size of chip area is 0.90x0.89 mm(2).