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

Abstract

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 SigmaDelta 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 SigmaDelta modulator can be improved at the same time. The order of the SigmaDelta 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 mum CMOS process. The size of the chip area is 0.44 times 0.48 mm2. 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.