應用於Serial-ATA之6GHz低相位抖動展頻時脈產生器之設計與實作

Abstract

EMI (Electro-Magnetic Interference) causes more destruction to the transmitting signal since the operating frequency is higher than before. Spread spectrum clocking (SSC) is a method that can reduce the EMI effectively. This method is more and more popular since it is easy to design and suitable for integrated IC. Serial ATA is a high speed external mass storage device having the SSC specifications as following: a triangular modulation profile with down spread, a 5000 ppm frequency deviation, a 30~33KHz modulation frequency, an EMI reduction larger than 7dB, and a 3ps RMS jitter @ 250 cycles. Our research is stressed on low-jitter design. Due to the higher operating frequency requirement, design with low-jitter performance becomes more and more important and thus more difficult to realize. VCO phase noise dominates the jitter performance of PLLs. Therefore, we proposed a LC tank VCO with low phase noise characteristic. The simulation results show that the phase noise is -119.8dBc/Hz @1MHz offset voltage and FoM is -190.8. In this Thesis, a spread spectrum clock generator (SSCG) modulated by a divider is presented. The PLL is fabricated in a 0.18μm CMOS process and the whole SSCG system is integrated and tested on an FPGA board. The simulation results show that all specifications of the Serial ATA have been achieved in our system and the jitter measurement shows that the RMS jitter is 0.4ps @ 250 cycles.