Low-jitter and Large-EMI-reduction Spread-spectrum Clock Generator with Auto-calibration for Serial-ATA Applications

A low jitter voltage-controlled oscillator (VCO) with high-frequency-limiter and an auto-calibration technique suitable for this VCO was developed for a spread-spectrum clock generator (SSCG). The high-frequency-limiter prevents the SSCG from going into an unlocked state. The proposed VCO achieved far less jitter than a conventional one because a proposed structure has less operating MOSs. The auto-calibration technique prevents the SSCG from degrading a performance caused by a process variation by controlling VCO gain and maximum output frequency. The auto-calibration SSCG was fabricated in a 0.13-mum CMOS process for serial-ATA applications. The variation in the rms jitter at 1.5 GHz with spread-spectrum clocking (SSC) is improved from 2.1-7.8 ps to 1.9-3.3 ps and the EMI reduction of 10.0 dB is achieved.