Spread-spectrum clock generator (SSCG) is a cost-effective solution to reduce EMI, which has become a serious problem in high-speed systems. In many applications, including serial links, display drivers and consumer electronics, SSCG is essential or strongly recommended. Control options such as frequency deviation and modulation frequency help satisfy various demands of different applications. Efficient modulation profile and its generation are critical to achieving large EMI reduction and lowering fabrication cost. This paper provides a tutorial review of SSCGs. After reviewing various kinds of EMI reduction technique, the SSCG that has cost-effective nonlinear modulation profile generator is presented. The SSCG can support 14 frequency deviations and three modulation frequencies. It achieved and EMI reduction of 19.14dB with a 5000ppm down spreading and a 31kHz modulation frequency.