What Is a Line Filter?

A filter is a filter circuit composed of a capacitor, an inductor, and a resistor. The filter can effectively filter out a frequency point of a specific frequency in the power line or a frequency outside the frequency point to obtain a power signal of a specific frequency, or eliminate a power signal of a specific frequency.

A filter is a frequency selection device that can pass specific frequency components in a signal and greatly attenuate other frequency components. With this frequency selection effect of the filter, interference noise can be filtered or spectrum analysis can be performed. In other words, any device or system that can pass specific frequency components in a signal and greatly attenuate or suppress other frequency components is called a filter. A filter is a device that filters waves. "Wave" is a very broad physical concept. In the field of electronic technology, "wave" is narrowly limited to specifically describe the process of the fluctuation of various physical values over time. The process goes through various

The main parameters of the filter:

There are two types of analog filters and digital filters according to the processed signals.

There are five types of low-pass, high-pass, band-pass, band-stop, and all-pass filters according to the frequency band of the passed signal.

Low-pass filter: It allows low-frequency or direct-current components in the signal to pass, suppressing high-frequency components or interference and noise;

High-pass filter: it allows high-frequency components in the signal to pass, suppressing low-frequency or DC components;

Bandpass filter: It allows signals of a certain frequency band to pass, and suppresses signals, interference and noise below or above the frequency band;

Bandstop filter: It suppresses signals in a certain frequency band and allows signals outside the frequency band to pass, also known as a notch filter. ^[1]

Although the on-board filter is not ideal for high-frequency filtering, if properly applied, it can meet the electromagnetic compatibility requirements of most civilian products. Pay attention to the following when using:

If you decide to use the on-board filter, pay attention to leaving a "clean ground" at the cable port when wiring, and the filter and connector are installed on the "clean ground". From the previous discussion, we know that the interference on the signal ground is very serious. If the filter capacitor of the cable is directly connected to this ground, it will cause serious common-mode radiation problems. In order to obtain better filtering results, a clean ground must be prepared. And the signal ground can only be connected at one point. This circulation point is called a "bridge". All signal lines pass through the bridge to reduce the area of the signal loop.

Side by side setting: The unfiltered parts of all the wires in the same group of cables are together, and the filtered parts are together. Otherwise, the plutonium filtering part of one wire will re-contaminate the filtered part of the other wire9 and make the overall cable filtering ineffective.

Close to the cable: The distance between the filter and the panel should be as short as possible. If necessary, use a metal plate to block it to isolate near-field interference.

Connection to the chassis: The dry ground where the filter is installed must be reliably overlapped with the metal chassis. If the chassis is not metal, a larger metal plate is set under the circuit board as the filtering ground. The clean connection to the metal case should ensure a very low RF impedance. If necessary, use electromagnetic sealing gaskets to increase the overlap area and reduce the RF impedance.

Short ground wire: Considering the inductance effect of the pins, its importance has been discussed earlier. Particular wiring of the filter and the connection structure between the circuit board and the chassis (metal plate) must be paid special attention.