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Why is the actual filter like this?
Sep 01, 2018

Why is the actual filter like this?

The actual power supply filter is basically a band-stop filter, mainly capacitors and inductors are not ideal. The leads of the capacitor are inductive, and there are parasitic capacitances on the inductor. Although these inductors and capacitors are small, their effects are not negligible when the frequency is high. Therefore, the low-pass filter circuit composed of the actual inductor and capacitor becomes a band-stop filter circuit when the frequency is high. It follows that the low-pass power supply filter is actually the ideal power supply filter.

In addition, the coupling between devices at high frequencies is also a cause of the insertion loss of the filter in the high frequency range. Because the distance between the devices has a large impact on the high frequency performance of the filter. This effect is already evident at 1MHz. Therefore, even if the circuit structure of the filter is completely the same, the high frequency performance of the device will be much worse due to the different characteristics of the device, the different mounting methods of the device, and the internal structure. The circuit structure of the filter only determines the low frequency characteristics of the filter. In order to improve the high-frequency performance of the filter, it is necessary to pay attention to the manufacturing process from many aspects, such as selecting a capacitor with a small inductance, making an inductor with a small parasitic capacitance, making the lead of the capacitor as short as possible, and taking appropriate isolation inside.

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