推荐回答（3个）
示波器的底噪即示波器的本底噪声，一般指示波器在测量中与信号存在与否无关的一切干扰，主要是由示波器的衰减器，前端放大器以及模数转换器产生。
我们通过设置来看看带宽、采样率、存储深度这示波器的三大指标对底噪的影响。
我们打开示波器的带宽限制，将其设置为20M，可以看到此时的底噪在500μV左右。难道带宽越低的示波器底噪反而越小吗？由于噪声信号基本都是高频信号，当示波器带宽太低的时候，就无法捕捉到那些高频信号，因此就会显得底噪小。同样的，示波器的带宽越高，采集到的信号谐波分量越丰富，往往噪声也会越大。为了避免这种高带宽引入的干扰，有的示波器在高灵敏度垂直挡位下会自动进行带宽限制，以此使得测量出来的波形更加清晰。
我们知道示波器的采样率 = 存储深度 ÷ 波形记录时长，示波器采集的数据点越多，对波形的重构自然就越完整，因此低采样率肯定也会使得底噪的显示变低，当然低采样率也可能导致我们想要采集的信号失真，具体多少采样率足够，可以参考我们之前的文章：示波器测各种类型信号需要多大采样率实测
我们将示波器的存储深度调节为28K，此时的采样率为20MSa/s，可以看到底噪的峰峰值为683.8μV。
总结来说，示波器的带宽越高，采样率越高，往往底噪也会显示的越高，但这并不是说低带宽的示波器引入的噪声就小，而是有很大一部分信号没有被捕捉到而已。因此，我们在对示波器进行底噪比较的时候，要保证2个示波器的各项设置和参数一致，才具有比较的意义。
以下是示波器底噪的测量方法：1、确保示波器是在正常的运行状态下；2、使示波器不接探头或示波器探头BNC端与地端短接；3、设置合适的水平时基档位和垂直时基档位（一般都是非常灵敏的档位，如2mv/div，1us/div等）；4、短按【Trigger】旋钮，调整触发电平，使底噪波形稳定显示；5、由于示波器屏幕上显示的是噪声的峰值偏移，所以对于底噪最直观的测量参数就是峰峰值测量。按下【Measure】选择“峰峰值”测量即可。我们可以通过对比，来看看现在市面上比较火热的三个品牌示波器的底噪是怎样的。在水平时基档位为2us/div，垂直档位时基为2ms/div下，MSO4054示波器（采样率为500MSa/S）测得峰峰值平均值为1.60mV，而ZDS2022示波器（采样率为1GSa/S）的峰峰值平均测量为351uV。从理论上说，采样率越高，波形细节越清晰，底噪应该越大，但从测量结果可知，ZDS2022示波器的底噪明显优于MSO4054示波器。 图Tek公司的MSO4054底噪 图 ZDS2022示波器底噪 由图所示，水平时基档位设置为100us/div，垂直时基档位设为2mv/div，并且两示波器都开启无限余辉模式。ZDS2022示波器（带宽200MHz，采样率1GSa/s）测得峰峰值平均值为449uV，而MSO-X3012A（带宽100 MHz，此时采样率也为1GSa/s）测得峰峰值平均值为1.6529mV。从理论上说，当带宽越高时，采集到的信号谐波分量越丰富，底噪应该越大，但从测量结果可知，ZDS2022示波器的底噪同样优于安捷伦的MSO-X3012A示波器。
示波器的底噪和示波器本身内部电路以及当前的设置有关，当前设置主要包括存储深度，时基，采样方式等等。
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