A Spread Spectrum Clock Generator with Controllable Frequency Modulation Profile

Abstract

In this paper, a spread spectrum clock generator (SSCG) with controllable frequency modulation profile is presented. The electromagnetic interference (EMI) suppression can be improved by changing the frequency modulation profile without altering the spread ratio or modulation frequency. The frequency modulation profile is controlled from triangular to sawtooth by changing the slope of the modulation profile using simple digital logic. The proposed SSCG is designed using a 0.18-㎛ CMOS process technology. Phase-locked loop, phase interpolator-based frequency modulator, and digital logic are used for implementing the proposed SSCG. The performance is verified with HSPICE simulation. The output frequency, down spreading deviation, and modulation frequency are 270 ㎒, 1.54%, and 33 ㎑, respectively. Simulation results show that EMI suppression is controlled from 18.01 ㏈ to 20.26 ㏈ according to the frequency modulation profile. The simulated power consumption of the proposed SSCG is 7.7 ㎽ at the supply voltage of 1.8 V.