为使高速模数转换器发挥最高性能，必须为其提供干净的直流电源。高噪声电源会导致信噪比(SNR)下降和/或ADC输出中出现不良的杂散成分。本文将介绍有关ADC电源域和灵敏度的背景知识，并讨论为高速ADC供电的基本原则。
模拟电源和数字电源
当今的大部分高速模数转换器至少都有两个电源域：模拟电源(AVDD)和数字与输出驱动器电源(DRVDD)。一些转换器还有一个附加模拟电源，通常应作为本文所讨论的额外AVDD电源来处理。转换器的模拟电源和数字电源是分离的，以防数字开关噪声(特别是输出驱动器产生的噪声)干扰器件模拟端的模拟采样和处理。根据采样信号的不同，此数字输出开关噪声可能包含显著的频率成分，如果此噪声返回器件的模拟或时钟输入端，或者通过电源返回芯片的模拟端，则噪声和杂散性能会很容易受其影响而降低。
对于大多数高速模数转换器，建议将两个独立的电源分别用于AVDD和DRVDD。这两个电源之间应有充分的隔离，防止DRVDD电源的任何数字开关噪声到达转换器的AVDD电源。AVDD和DRVDD电源常常采用各自的调节器，然而，如果在这两个电源之间实现了充分的滤波，则采用一个调节器通常也能获得足够好的性能。
ADC电源灵敏度——PSRR
确定高速ADC对电源噪声的灵敏度的一个方法，是将一个已知频率施加于转换器的电源轨，并测量转换器输出频谱中出现的信号音，从而考察其电源抑制性能。输入信号与输出频谱中出现的信号的相对功率即为转换器在给定频率下的电源抑制比(PSRR)。下图显示了典型高速ADC的PSRR与频率的关系。此图中数据的测量条件是将器件安装于配有旁路电容的评估板上，这种方法能够显示典型应用中器件如何响应电源噪声。注意在这种情况下，转换器的PSRR在低频时相对高得多，当频率高于约10MHz时会显著下降。
利用此PSRR信息，设计人员可以确定为了防止噪声损害转换器的性能，电源所容许的纹波水平。例如，如果一个电源在500kHz时具有5mVp-p的纹波，则从下面的PSRR图可知，转换器在此频率提供大约58dB的抑制。转换器的满量程为2Vp-p，因此原始5mV信号比输入满量程低52dB。此信号将进一步衰减58dB，从而比转换器的满量程功率低110dB。这样，设计人员就能使用转换器的PSRR数据来确定在给定频率下转换器电源的容许纹波。如果转换器的电源在已知频率具有纹波，例如来自上游开关转换器，则可以利用该方法确定将此噪声衰减至容许水平所需的额外滤波。
上述分析假设给定电源上仅出现一个频率。事实上，根据电源获得方式的不同以及该电源供电对象的不同，电源上的噪声可能具有额外频率成分。如果是这种情况，设计人员必须确保为电源提供充分的滤波来衰减此噪声。请注意，由于ADC输入的宽带特性，在其它奈奎斯特频率区中，处在ADC输入的目标频带之外的噪声可能会进入目标频带。
关于线性调节器的讨论
传统上使用线性调节器来为转换器的AVDD和DRVDD轨提供干净的电源。低压差线性调节器能够出色地抑制约1MHz以下的低频噪声。典型LDO的控制环路带宽不超过此频率，因此更高频率的噪声会几乎毫无衰减地通过调节器。对于此频率以上的噪声，必须在LDO之后通过额外滤波对其进行衰减，防止此噪声到达 ADC。通常，结合使用铁氧体磁珠、大去耦电容" title="去耦电容" target="_blank">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" 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title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" 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title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容" title="去耦电容">去耦电容">去耦电容和局部电源去耦，即足以衰减任何通过线性调节器的高频噪声。设计电源滤波器时必须注意，如果使用串联感性元件，应确保上电和掉电时的感应电势不会达到足以损坏转换器的水平。
图1：典型ADC电源抑制比与频率的关系
此外，鉴于LDO的上游常常还会有一个开关转换器，设计人员必须确保LDO和滤波器电路能够充分抑制此开关转换器的频率。现代开关转换器的开关频率越来越高，可能高于典型LDO的环路带宽。来自这些高频开关转换器的噪声很容易通过LDO，必须利用下游滤波器对其进行衰减。
虽然线性调节器能够很好地为ADC提供干净的电源，但效率不高是其主要缺点。根据提供给线性调节器输入端的电压的不同，LDO的效率可能非常低。提供一个略高于LDO压差的电压虽然可以提高效率，但这经常需要增加额外的电源级，导致电源设计的成本和复杂度随之增加。
关于开关调节器的讨论
传统上，开关调节器不宜用于直接为ADC供电。然而，开关调节器技术已今非昔比，当与后置滤波、精心的设计和布局布线做法相结合，开关调节器可以用作许多高速模数转换器的高效率电源解决方案。如图2所示，开关调节器的效率可达95%，相比于LDO，系统功耗显著降低。对于一个功耗为780mW的1.8V单电源ADC，如果使用开关调节器电源，整体系统功耗可降低640mW或更多。此外，开关电源设计消除了线性级这一热源，PCB的总体热量得以降低，因而对风扇和散热器等额外冷却措施的需求会减少。
图2：LDO为ADC供电，包括滤波
不过，开关调节器确实会产生噪声，必须通过精心的设计和布局布线予以控制。开关电源主要有两类噪声：开关纹波和高频噪声。对于恒频开关调节器，开关纹波会在开关频率及其倍数频率产生能量。高频噪声由转换器中的电压和电流快速跳变而产生。1-5ns的典型上升时间可以在70-350MHz区间内产生能量。对这两个噪声源均必须进行充分滤波，以免其干扰转换器的工作，降低转换器的性能。这可能需要使用多级LC滤波器，以降低纹波并衰减噪声。为保持直流调节能力，开关电源控制环路可以在输出滤波器的两级附近闭合。为保持稳定性，环路穿越频率必须较低。ADC给电源带来的负载特性基本上是一个与时钟频率成正比的直流负载。由于该负载是恒定的，开关调节器的瞬态响应相对不重要，因此低环路穿越频率在这种情况下是可以接受的。对调节器进行外部补偿可以更轻松实现这一目标。
对输出电源电压上的噪声进行充分滤波至关重要，但设计人员也必须尽量减小从电源所含磁性元件(电感)到与ADC时钟或信号路径相关的巴伦或变压器之间的磁场或电场耦合。将电源电感放在PCB上的另一端并远离关键的ADC时钟和输入相关电路，有助于减小这种耦合。
电源去耦
尽管高速ADC给电源带来的总负载是稳定的，但需要电流以ADC采样速率和此频率的谐波快速跳变。由于电路板和走线的电感会限制电源能够迅速提供的电流量，因此ADC所需的高频电流是由板电源去耦电容提供的。为高速ADC供电时，应同时采用大的电源去耦电容和局部(ADC引脚处)去耦电容。大去耦电容存储电荷以对电源层和局部去耦电容充电，局部去耦电容则提供ADC所需的高频电流。有效的去耦还能将高频电源瞬变限制在距离产生瞬变的IC非常近的区域，从而使电路板上产生的电磁辐射(EMI)降至最小。
图3：开关调节器的典型效率
一般而言，应为每个ADC电源轨至少提供一个大去耦电容。这些电容应当是10uF至22uF范围内的低ESR陶瓷或钽电容。对于局部去耦，一般建议为每个电源引脚提供一个去耦电容。局部去耦电容应当是0.01uF至0.1uF范围内的低ESR陶瓷电容，并且应尽可能靠近ADC电源引脚放置。这些电容应具有通向电源层的过孔，并且过孔应非常靠近ADC电源引脚。如果ADC是从PCB上紧密耦合的电源层获得电源，则局部去耦也可以通过层与层之间的电容效应实现。如果这些层相对较大，并且间隔小于5密尔(mil)，则层间电容可提供非常有效的去耦作用。层间电容与局部旁路电容共同提供ADC所需的高频电流。
接地
ADC接地是电源方案的重要一环。当前许多ADC都采用LFCSP封装，封装底部有一个接地金属块。此金属块用于为器件散热；在许多情况下，此接地金属块是器件唯一的接地连接。必须将此接地金属块焊接到电路板上的接地焊盘，此焊盘有多个过孔通向接地层。
ADC地上的噪声也会影响其性能。当数字回路电流流经ADC所在区域时，通常会产生接地噪声。设计人员应当采取措施，确保高噪声地电流不会流经ADC附近。一般建议使用连续层，但为了隔离高噪声地电流，可能需要使用非连续层。
结论
ADC 的电源实现方案可能会对器件的性能产生重大影响。按照本文提出的指导原则进行设计，可以实现有效的ADC电源。寻找特定ADC的电源参考资料时，首先应查看该ADC的评估板。ADI公司的所有ADC都有附带电源的评估板。研究评估板电源的结构以及它所采用的去耦和布局，是开展ADC电源设计的最好起点。
