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首页> 外文期刊>Circuits and Systems I: Regular Papers, IEEE Transactions on >On Pulse Position Modulation and Its Application to PLLs for Spur Reduction
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On Pulse Position Modulation and Its Application to PLLs for Spur Reduction

机译：脉冲位置调制及其在降低杂散的PLL中的应用

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摘要

Randomizing the positions of charge pump current pulses in a PLL breaks their periodicity and redistributes the reference spurs into broadband noise. Closed form expressions for the power spectral density (PSD) of pulse position modulated (PPM) signals are derived and intuitive explanations for the results are given. The redistributed noise has a high-pass shape and does not affect the close in phase noise of the PLL. PPM using a uniformly distributed i.i.d. sequence completely removes the spurs and provides a first-order shaping of redistributed noise. Higher order shaping and reduction of redistributed noise at intermediate offset frequencies are possible using PPM with a high-pass shaped modulating sequence and pulse repetition. Circuit implementations of these techniques are given and their nonidealities are discussed. Simulation results from a 1 GHz PLL operating from a reference frequency of 20 MHz and a bandwidth of 1 MHz confirm the results of the analysis and viability of the proposed techniques. In the presence of nonidealities spurs can be reduced by at least 13 dB without any trimming of the delays in the PPM circuits and by 25 dB after trimming the delays to within 5% of the nominal value.
机译：将PLL中的电荷泵电流脉冲的位置随机化会破坏其周期性，并将参考杂散重新分配到宽带噪声中。推导了脉冲位置调制（PPM）信号的功率谱密度（PSD）的闭式表达式，并对结果给出了直观的解释。重新分配的噪声具有高通形状，并且不会影响PLL的封闭相位噪声。使用均匀分布的i.d.的PPM序列完全消除了杂散，并提供了重新分布噪声的一阶整形。使用具有高通整形调制序列和脉冲重复功能的PPM，可以在中等偏移频率处进行更高阶的整形并降低重新分配的噪声。给出了这些技术的电路实现，并讨论了它们的非理想性。 1 GHz PLL在20 MHz参考频率和1 MHz带宽下工作的仿真结果证实了所提出技术的分析结果和可行性。在存在不理想的情况下，杂散可以减少至少13 dB，而不会对PPM电路中的延迟进行任何调整，而在将延迟调整至标称值的5％以内后，则可以降低25 dB。

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