有源滤波器控制EMI，节省PCB空间，增强气流。

　　有源滤波器控制EMI，节省PCB空间，增强气流。

　　当空间缩小时，干扰的可能性增大。

　　在较小的空间中具有更多功能的小型设备的趋势在电子工业中有增无减。当空间缩小时，设备间干扰的可能性增加，因为系统在密集的板和机架中满足更多的功能。随着频率的增加和电压水平的下降，传导EMI的控制成为一个更重要的设计任务。

　　EMI控制是一个复杂的设计任务，它高度依赖于许多设计元素，利用无源和有源滤波器来管理传导噪声。有源EMI滤波器，与无源解决方案相反，减少共模扼流圈的体积，允许滤波器被封装在1×1“x 0.2”包中，并提供低轮廓的表面贴装器件。较小的尺寸节省宝贵的板房地产，减少高度提高气流更好的热管理。

　　Active EMI filters （labeled QPI in Figure 1） attenuate conducted-mode and differential- mode noise over the frequency range of 150 kHz to 30 MHz required by conducted emissions standard EN55022 （CISPR22）。 Figure 2 shows before and after plots of a DC-DC converter noise profile to demonstrate the performance of an active filter. The plots were taken using the standard measurement technique， and were set up as defined in CISPR22. The results show the total noise spectrum for a standard DC-DC converter under load， compared to the EN55022 Class B Quasi-peak detection limit. The plot shows that an active filter is effective in reducing the total conducted noise spectrum to well below the required limits.