A Spread Spectrum Clock Generator with Dual-tone Hershey-Kiss Modulation Profile

Abstract

This paper presents a spread spectrum clock generator (SSCG) using a dual-tone Hershey-Kiss modulation profile. The modulation controller has two up/down counters and one delta-sigma modulator, and the output of the modulation controller is provided to a multi-modulus divider in a fractional-N PLL. The proposed SSCG is designed to operate in either single-tone modulation mode or dual-tone modulation mode. Once the targeted modulation frequency and spread ratio are given, the design variables for the SSCG can be controlled digitally. The proposed SSCG was designed and fabricated using the 65 nm CMOS process and consumes 8.5 mW while generating a 5 GHz spectrum-spread clock signal with 1.2 V supply voltage. After all design parameters are set for a 0.5% spread ratio using 30 and 33 kHz modulation frequencies, the measured EMI reduction is 24.6 dB while single-tone modulation is applied and 28.7 dB while dual-tone modulation is applied.