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Author:Site Editor Publish Time: 2020-12-30 Origin:Site

The filter is a filter circuit composed of capacitors, inductors and resistors. The filter can effectively filter out the frequency point of a specific frequency in the power line or the frequency other than the frequency point to obtain a power signal of a specific frequency, or eliminate a power signal of a specific frequency.

According to the frequency selection function of the filter, the filter can be divided into four categories: low-pass, high-pass, band-pass, and band-stop filters.

If only considering the frequency spectrum part whose frequency is greater than zero, the amplitude-frequency characteristics of these four filters are shown in the figure.

The signal from the filter is no longer sent to the next circuit, and the signal from the frequency selector is sent to the next circuit.

Just like sugar, when used to make candies, sugar is the main ingredient; when used in cooking, sugar is the auxiliary material. Similarly, some electronic components are used in filter circuits as filters, and used in wave selector circuits as wave selectors. . The difference mainly depends on whether the output signal is useful or not. The former is sent to the next level, the latter is not sent to the next level, or directly into the ground.

The frequency selector is a type of filters, such as low pass, bandpass, bandstop, high pass, and other filters. Filters can be used for frequency selection, waveform shaping, such as Gaussian filters, and model predictions, such as adaptive filters.

The filter has the following functions:

Function: The filter is a circuit or arithmetic processing system with a frequency selection function, which has the function of filtering noise and separating various signals.

Type: According to the form of processing signal: analog filter and digital filter according to function: low pass, high pass, bandpass, band stop. According to circuit composition: LC passive, RC passive, passive filter composed of special components According to the order of the differential equation of the transfer function, the filter, and RC active filter is divided into first-order, second-order, high-order

The transfer function and frequency characteristics of the analog filter: the transfer function of the analog filter The characteristics of the analog filter circuit can be described by the transfer function. The transfer function is the ratio of the output to the input signal voltage or current Laplace transform. After analysis, after any number of isolated linear networks are cascaded, the total transfer function is equal to the product of each network transfer function.

In short, the filter is used to filter out the clutter. The purpose of filtering clutter is to obtain the desired waveform.

The comb filter consists of many passbands and stopbands arranged in the same frequency interval, and only passes signals in certain specific frequency ranges.

The characteristic curve of the comb filter is like a comb, so it is called a comb filter.

Except for occasions with special requirements, most digital TV equipment or high-quality digital TV receivers use line-delayed comb filters and band-pass filters in cascade to form a Y, C separation scheme to obtain satisfactory image quality.

One type of magnetic core often used in filters is ferrite magnet material. Ferrite material is specially used for electromagnetic interference suppression. This material is characterized by very large high-frequency loss and high magnetic permeability. It can be the smallest capacitance between the coil windings of the inductor under high-frequency and high-resistance conditions. For ferrites used to suppress electromagnetic interference, the most important performance parameters are permeability μ and saturation magnetic flux density Bs. Permeability μ can be expressed as a complex number, the real part constitutes the inductance, and the imaginary part represents the loss, which increases with the increase of frequency. It is a function of frequency such as resistance R(f), and f represents frequency.

In the low-frequency band, the impedance is composed of the inductive reactance of the inductor. At low frequencies, R is very small, and the magnetic permeability of the magnetic core is high, so the inductance is large, the inductance plays a major role, the electromagnetic interference is reflected and suppressed, and the loss of the magnetic core is small at this time, and the whole device is a low loss, High-quality factor Q characteristic inductance, this kind of inductance is easy to cause resonance, so in the low-frequency band, sometimes the phenomenon of interference enhancement after using ferrite beads may occur. Therefore, a small resistor is often connected in series in the actual circuit to eliminate resonance.

In the high frequency range, impedance is composed of resistance components. As the frequency increases, the permeability of the magnetic core decreases, the inductance of the inductor decreases, and the inductive reactance component decreases. At this time, the total impedance of the magnetic core increases. When the high-frequency signal passes through the ferrite magnet, electromagnetic interference is absorbed and converted into heat energy to be dissipated.

Ferrite suppression components are widely used in printed circuit boards, power lines and data lines, or to suppress diode reverse recovery current spikes. For example, adding ferrite suppression components at the entrance of the power cord of the printed board can filter out high-frequency interference. The ferrite bead or bead is specially used to suppress high frequency interference and spike interference on signal lines and power lines. It also has the ability to absorb electrostatic discharge pulse interference.

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