This article describes the cross-correlation function as an alternative method to adapt loop gain in digital CDRs. Cross-correlation function inherent properties and their link with the cross-power spectral density help consolidating the adaptive loop gain technique, XCALG, for clock and data recovery systems that implement bang-bang phase detector. Considering the modulation of the loop gain due to jitter noise, previous works exploit the autocorrelation function at the output of the bang-bang phase detector as a proper indicator to track the system dynamics and perform loop gain adaptation. In contrast, we propose the XCALG as a new alternative to perform loop gain adaptation featuring better observability, less impact from jitter sources while keeping a safe phase margin. Theory behind the idea is enhanced, and the XCALG is demonstrated through behavioral system simulations. In addition, preliminary implementation costs of the cross-correlation function are discussed using a 65nm CMOS technology node.

中文翻译：

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基于互相关的 Bang-Bang CDR 环路增益自适应

本文将互相关函数作为一种替代方法来适应数字 CDR 中的环路增益。互相关函数的固有属性及其与交叉功率谱密度的联系有助于巩固自适应环路增益技术 XCALG，用于实现 bang-bang 相位检测器的时钟和数据恢复系统。考虑到由于抖动噪声引起的环路增益调制，以前的工作利用 bang-bang 相位检测器输出端的自相关函数作为跟踪系统动态和执行环路增益自适应的适当指标。相比之下，我们建议 XCALG 作为执行环路增益自适应的新替代方案，具有更好的可观察性、更少的抖动源影响，同时保持安全的相位裕度。这个想法背后的理论得到了加强，XCALG 是通过行为系统模拟来演示的。此外，使用 65nm CMOS 技术节点讨论了互相关函数的初步实现成本。