A Low-Power and High-Precision Spread Spectrum Clock Generator for Serial Advanced Technology Attachment Applications Using Two-Point Modulation

A new technique utilizing two-point (TP) modulation for a spread spectrum clock generator (SSCG) for serial advanced technology attachment is presented in which the divider ratio is varied by a digital ${Sigma}{Delta}$ modulator, and the voltage-controlled oscillator is modulated analogically. With this technique, the modulation bandwidth is enhanced in order that the modulation profile accuracy and jitter performance caused by the ${Sigma}{Delta}$ modulator can be improved at the same time. The order of the ${Sigma}{Delta}$ modulator and the loop filter can be reduced to save power and area, while the electromagnetic interference (EMI) suppression still satisfies specifications. The dual-path loop filter (DL) reduces the size of the loop capacitor and enables full integration. The proposed TPDL-SSCG has been fabricated in a 0.18- $mu$m CMOS process. The size of the chip area is $hbox{0.44} times hbox{0.48 mm}^{2}$. The circuit produces a clock of 1.5 GHz with a down-modulation ratio of 0.5%, 10.14 dB EMI of reduction, 5.485 ps rms jitter, and 35 ps peak-to-peak jitter. The power consumption, excluding an output buffer, is only 15.3 mW.