A Spread Spectrum Clock Generator For SATA With Programmable Triangular Modulator
Date Issued
2009
Date
2009
Author(s)
Chia-Tseng ,Chiang
Abstract
As external storage devices are widely used, high-speed serial links connection host and external devices are becoming popular. Serial AT Attachment (SATA.) is one of the most promising technologies providing large bandwidth up to 3Gb/s with possible extension to 6Gb/s in the near future. As operating a high speed data rate, currents and voltages present in the circuit and the signal traces lead to great Electro-Magnetic Interference (EMI), Therefore, SATA systems require a wide spreading of 5000ppm and a 30~33KHz modulation rate to reduce EMI. Spread spectrum is a special frequency modulation technique, which is sacrificed the signal integrity of the clock to reduce the EMI. In this thesis, we proposed a novel spread spectrum clock generator (SSCG) to release the trade-offs between the jitter performance and the amount of EMI reduction for SATA appications. Besides considering the amount of EMI peak reduction in frequency-domain, it is more important to take care of the impact in time-domain for SSCGs since the signal integrity in time-domain is a very significant issue for serial data transmissions. This chip is implemented in the process of 0.18um CMOS. In chapter 4 we proposed a programmable triangular generator technique for SSCG (Down spread 2500ppm~ 5000ppm). The technique utilizes the digital data stored in up/down counter to control the spread spectrum amount. An integer-N frequency synthesizer (low frequency) supplies the up/down counter clock to maintain the modulation frequency. Therefore we can adjust spread spectrum amount dynamically to achieve an optimal value between EMI reduction amount and the performance of jitter.
Subjects
Spread Spectrum Clock Generator
programmable triangular generator
Up/Down counter
Electro-Magnetic Interference
integer-N frequency synthesizer
Type
thesis
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