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Filter structure
Sep 04, 2018

Filter structure

The function of the filter is to have different amplification effects for different frequencies passing through it, and the frequency band in the passband is not attenuated, and the suppression outside the passband is attenuated by a level of several tens of dB, thereby achieving the sifting. purpose. However, when the filter adopts different amplification factors for voltage amplitudes of different frequencies, the phase of the electromagnetic wave also changes. Since the phase is also related to the frequency, the selection of the filter structure is still somewhat learned. There are three common types of filter structures:

1. Butterworth filter

The characteristic is that the amplification factor in the passband is flat. In the passband, the filter magnification remains basically unchanged with the change of the frequency; but the disadvantage is that the transition from the passband to the cutoff section is relatively smooth. It means that the boundaries between the enemy and the friends are not very clear. Some of the friends are also doing the enemy's things. Some of the enemies are also helping us. Whether this part is killed or left in the organization is very tangled. If the useful frequency and the interference frequency are close together, the effect of this filter is problematic.

2. Chebyshev filter

It can well solve the shortcomings of the Butterworth transition zone. In this type of filter, the transition zone is steep, even if the useful frequency and the interference frequency are very close, because the transition zone is steep, its cutoff frequency point is around The difference between the two frequency bands is very large. The non-friends are the enemy, which is very good. It is a friend who has never done anything that is sorry for us. It is the enemy who has never done anything good for us, so the friend pulls in the organization. It is the enemy that is clean and neat. There must be deep valleys on the side of the mountain. One advantage must be accompanied by a disadvantage. The shortcoming of the Chebyshev filter is that at the end of the passband frequency, the amplification factor will have strong fluctuations, that is, in the passband, with the frequency Although the magnification is much larger than the filtering frequency band, the magnification of the frequency in the passband is not stable. That is to say, the emotions of the friends are not stable, and not all friends are as always. Give help. (Only for illustration, don't misunderstand as dissatisfaction with friends)

3. Bessel filter

This type of filter is not very versatile and is more specialized because its characteristic is phase linear. The first two focus on magnification, but if there is no change in the magnification of the voice signal, such as a song, the melody is no longer melodious. Because of the change in phase, it is difficult to listen to the song. At this point, the Bessel filter will have its effect.

Tips: Choose which filter circuit structure form, circuit engineers do not necessarily do in-depth research, but must know the characteristics they want, and provide them to the filter manufacturers, who can help you make choices.

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