What does the order and length of a filter mean?

The order of a filter refers to the number of harmonics to be filtered. Generally speaking, for the same filter, the higher the order, the better the filtering effect, however, the higher the order, the higher the cost, so it is very important to choose the right order.

The length of the filter refers to the bandwidth of the filter. For example, we produce special filters for inverters, the filtering range is 10K ~ 30MHz; from this point of view, the wider the filtering range of the filter, the better, the same, but also need to consider the cost of the problem, the right, is the best.

The main parameters of the filter:

Center Frequency (Center Frequency): the frequency of the passband of the filter f0, generally taken as f0 = (f1 + f2)/2, f1, f2 for the band-pass or band-stop filter left, right relative to the decline in the frequency of the 1dB or 3dB side frequency point. Narrow-band filters are often calculated with the insertion loss minimum point as the center frequency of the passband bandwidth.

Cutoff Frequency: The right frequency point of the passband of a low-pass filter and the left frequency point of the passband of a high-pass filter. It is usually defined by 1dB or 3dB relative loss point as standard. The reference point for relative loss is the DC insertion loss for low-pass, and the insertion loss for high-pass at a sufficiently high passband frequency where no parasitic blocking band occurs.

Passband width: the width of the spectrum to be passed, BW = (f2-f1). f1, f2 is based on the insertion loss at the center frequency f0.

Insertion Loss: due to the introduction of the filter on the circuit of the original signal brought about by the attenuation, to the center or cut-off frequency at the loss characterized, such as the requirements of the full-band insertion loss needs to be emphasized.

Expanded Information

The on-board filter is not ideal for high-frequency filtering, but if properly applied, it can meet the electromagnetic compatibility requirements of most civilian products. In the use of the following matters should be noted:

If you decide to use the on-board filter, in the cabling should pay attention to the cable port to leave a piece of "clean ground", the filter and connectors are installed in the "clean ground".

Through the previous discussion, it can be seen that the interference on the signal ground is very serious. Connecting the cable's filter capacitors directly to such a ground can cause serious ****-mode radiation problems. In order to obtain a better filtering effect, a clean ground must be prepared. And with the signal ground can only be connected at one point, this circulation point is called "bridge", all signal lines are passed from the bridge to reduce the signal loop area.

Side-by-side setting: the same group of cables within all the wires of the unfiltered part of the - together, the filtered part of the together. Otherwise, the filtered portion of one wire will recontaminate the filtered portion of another wire, rendering the overall cable filtering ineffective.

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

Baidu Encyclopedia - Filters