A Novel Spread Spectrum Clock Generation Technique: Always-On Boundary Spread SSCG

Abstract

Spread spectrum clock generation (SSCG) is an important technique for electromagnetic interference reduction. To achieve the goal of lowering peak power, clock signal is intentionally “jittered.” In circuit implementation, there are mainly three ways to carry out the task of jittering the clock: voltage-controlled oscillator modulation, phase-locked loop divider dithering, and clock-period direct manipulation. From the perspective of spread result, there are three types including down spread, central spread, and up spread. Being an effective solution for lowering the harmful electromagnetic peak power, SSCG is also faced with a challenge of preserving the integrity of the clock signal. In this paper, a novel approach of always-on boundary spread is presented. It is based on time-average-frequency concept. Its aim is to maximize frequency modulation depth while precisely controls clock's impact on system operation. Theoretical analysis is performed, experimental validation is provided through an implementation on field programmable gate array (FPGA). Furthermore, a commercial product is used to demonstrate the feature of “always on” enabled by this SSCG technology.