书名：Chapter 12: Delta-Sigma Fractional-N Phase-Locked Loop

著作类别：Book Chapters

作者：Xueyi Yu, Woogeun Rhee, Zhihua Wang

出版地：USA

出版社：McGraw Hill Publishers

出版日期：2011-07-19

ISBN：9780071755658

内容简介：
        Offering high resolution by digital modulation, the ΔΣ fractional-N PLL can employ higher reference clock frequency and lower division ratio for the same output frequency. As a result, it alleviates several design trade-offs which could not be overcome in conventional integer-N PLL design. Although it plays a key role in modern wireline/wireless systems, the ΔΣ fractional-N PLL suffers from quantization noise, which will degrade the overall phase noise performance if it is not sufficiently suppressed. Therefore, there have been many studies focusing on the quantization noise reduction in recent years. This chapter begins with a brief introduction of ΔΣ fractional-N PLL basics, followed by descriptions of quantization noise and nonlinearity issues. Three existing methods for quantization noise reduction are reviewed, and the pros and cons of each method are discussed. After that, a hybrid FIR noise-filtering method based on a semidigital approach is proposed. It employs multiple phase detectors and dividers in parallel, which are controlled by the sequential output of the ΔΣ modulator. An FIR filtering effect is achieved with regard to the quantization noise when all the phase errors are summed up at the multi-input charge pump. Detailed theoretical analyses of this method are given, along with two hardware examples. The measurement results show that the proposed method can effectively reduce out-of-band quantization noise to improve the short-term jitter performance for digital clock generation in wireline application, while it is also able to achieve customized noise shaping to meet the phase noise mask requirement in a wireless application.

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