Click image to view original image
Selection method
Several low pass prototype filters are the basis for designing filters based on modern network synthesis. All kinds of low pass, high pass, band-pass and band stop filters are derived from this characteristic. Because of this, the design of the filter is simplified and the precision is improved.
The ideal low-pass filter should be able to make all below the cut-off frequency of the signal through the lossless and all higher than the signal, the cut-off frequency should be infinite attenuation, thus presenting a rectangle in the amplitude frequency characteristic curve, so called rectangular filter (brick-wallfilter). Unfortunately, such an ideal feature can not be realized, and all the designs are merely a feature that attempts to approach the rectangular filter. According to the difference of the selected approximation functions, different responses can be obtained. Although the approximation function is varied, the "Butterworth response" or "Chebyshev response" is usually chosen in consideration of the use of the actual circuit.
The "Butterworth response" bandpass filter has a flat response characteristic, while the Chebyshev response bandpass filter has a steeper attenuation characteristic. So the specific selection of the characteristics needs to be determined according to the specific requirements of the circuit or system. However, the Chebyshev response filter is the most insensitive to component changes, and has good selectivity and good standing wave characteristics (located in the middle of the passband). Therefore, in general applications, Chebyshev response filter is recommended. Main classification
According to the signal processed, it is divided into two kinds: analog filter and digital filter.It is divided into four types: low pass, high pass, band pass and band stop filter, according to the frequency band of the signal.
Low pass filter: it allows low frequency or direct current component in the signal to suppress high frequency components or interference and noise.
High pass filter: it allows the high frequency component of the signal to pass through, to suppress low frequency or direct current component;
Bandpass filter: it allows a signal to pass through a certain frequency band to suppress signals, interference and noise that is lower or higher than that of the frequency band. Bandstop filter: it inhibits a signal in a certain frequency band and allows signals beyond the band to pass through.
The components are divided into two kinds of passive and active filters according to the components used.
Passive filter: a filter consisting only of passive components, which is made up of the principle that the reactance of capacitance and inductance changes with the change of frequency. The advantage of this type of filter is that the circuit is relatively simple, does not require a DC power supply, high reliability; the disadvantage is: band signal energy loss, load effect is obvious, easy to cause the use of electromagnetic induction inductor, inductance when large L filter volume and weight are large, do not apply in low frequency domain.
Active filter is composed of passive and active components. The advantage of this type of filter is: band signal not only energy loss, but also can be enlarged, the load effect is not obvious, multi connected mutual influence is very small, very easy to use simple method of cascade consisting of high order filter, and the filter has the advantages of small size, light weight, need magnetic shielding; the shortcoming is: the pass band range of active devices need bandwidth limit, DC power supply, high reliability as the passive filter, is not applicable in high voltage, high frequency and high power applications. According to the different placement position of the filter, it is generally divided into board filter and panel filter. The board filter is installed on the circuit board, such as the PLB and JLB series filters. The advantage of this filter is economic and the disadvantage of high frequency filtering is poor. The main reasons are:
1. There is no isolation between the input and output of the filter, and it is easy to coupling.
2, the grounding impedance of the filter is not very low, which weakens the effect of high frequency bypass.
3, filter and a chassis line will have two effects: one is the electromagnetic interference in the interior space of the enclosure will directly to the induction line, along with cable cable from the chassis, radiation, the filter failure; the other is a disturbance before the plate filter, produced by radiation this section of the line, or directly on the circuit board and circuit coupling, resulting in the sensitivity problem;
The filter array board, filter connector and other panel filters are generally installed directly on the metal panel of the shielded chassis. Because it is directly installed on the metal panel, the input and output of the filter are completely isolated, the grounding is good, and the interference on the cable is filtered on the chassis port, so the filtering effect is quite satisfactory>
Having been sustained and stable growth, we always adhere to the scientific and humane management philosophy of making the best use of men and material and providing the best service wholeheartedly. Attach importance to a marketing idea of low profit brings a huge market. In the industry, we win a good reputation,Coalescer filter,Fuel Filterx1dd023en get praise from the majority of customers at home and abroad! Welcome friends from all walks of life come to visit, guidance and business negotiations. Official website: www.hqfiltration.com
