Dual-loop direct VCO modulation for spread spectrum clock generation

This paper presents a new spread spectrum clock generator (SSCG) circuit for EMI reduction. The proposed design adopts a standard integer-N phased locked loop (PLL) with two dual-voltage-controlled oscillators (VCOs). A frequency modulation loop is implemented with a digital frequency limit detector to direct the spectrum-spreading profile. An integrator is applied to generate the triangular modulation signal. Comparing with some recent designs in the literature, the spread spectrum clock generator in this paper is simple and area efficient.