A 3.5 GHz Spread-Spectrum Clock Generator With a Memoryless Newton-Raphson Modulation Profile

Abstract

A frequency-locked loop (FLL) based spread-spectrum clock generator (SSCG) with a memoryless Newton-Raphson modulation profile is introduced in this paper. The SSCG uses an FLL as a main clock generator. It brings not only an area reduction to the SSCG but also the advantage of having multiple frequency deviations. A double binary-weighted DAC is proposed that modulates the frequency information of the frequency detector using a 1-1-1 MASH Delta Sigma modulator. The Newton-Raphson mathematical algorithm is applied to the proposed profile generator in order to generate the optimized nonlinear profile without needing any memory, resulting in a reduction in the area and the power consumption. It also makes it possible to have multiple modulation frequencies. The SSCG can support 14 frequency deviations of to +/- 0.5% to 3.5% in steps of 0.5% and three modulation frequencies of f(m), 2f(m) and 3f(m). It achieved an EMI reduction of 19.14 dB with a 0.5% down spreading and a 31 kHz modulation frequency, while employing a core area of 0.076 mm(2) in a 0.13-mu m CMOS process and consuming 23.72 mW at 3.5 GHz.