In this paper, EMC rectification common problems, discuss, discuss trying to start a discussion.
First, the product diagnose the actual situation, analyze its sources of interference and where the ways and means of mutual interference. According to another analysis, targeted for rectification.
The main rectification general methods as follows.
1, reduced interference source, found on the basis of the interference source, interference may be reduced to allow the source range, the method is generally attenuated source follows:
a, between the Vcc and GND IC decoupling capacitors, the capacitor 0.01μF capacitance between 0.1FF date, note that when mounting the capacitor leads to make it as short as possible.
b, in the case of adding the attenuator to ensure that the sensitivity and signal to noise ratio. Such as VCD, DVD video disc in the crystal, its electromagnetic compatibility effects are more severe, reducing its amplitude is one feasible method, but it is not the only solution.
c, there is an indirect method of the signal line away from noise sources.
2, wire and cable classification finishing, in an electronic device, the coupling between lines is an important way, but also the major cause of interference, because the frequency factor, can be roughly divided into low and high-frequency coupler coupling. Depending coupling, which is different rectification method, are discussed below:
(1) low coupling, low coupling guide line is equal to or less than 1/16 the length of the wavelength, the coupling can be divided into low-frequency electric and magnetic coupling, electric field coupling physical model is a capacitive coupling, so the main object is to reduce the rectification distributed coupling capacitance or coupling amount decreases, the following method may be employed:
a, increasing the pitch of the circuit most effective way to reduce the distributed capacitance.
B, additionally a highly conductive shield, and the shield can effectively single point grounding reject the low frequency electric field disturbance.
c, the additional filter may reduce the amount of coupling between the two circuits.
d, to reduce the input impedance of, for example, high input impedance of the CMOS circuit, the electric field is extremely sensitive to interference, can
The allowed range and the input terminal connected to the internal low-value resistor or a capacitor. Physical model of the magnetic field coupling is an inductive coupling, coupled distributed mainly through mutual coupling between the lines, so the main method of destruction rectification or reducing the amount of coupling, the following method is generally employed:
a, additional filters, when the filter is to be noted additional input and output impedance and frequency response of the filter.
B, reducing the sensitivity of the loop circuit and the source area of the loop, i.e., as much as possible the signal line or the return line with its current line or twisted in close integrally.
C, increasing the spacing of two circuits, so as to reduce the line to reduce the mutual coupling amount.
d, if possible, try to make the circuit sensitive to the source circuit plane orthogonal or nearly orthogonal to reduce the amount of coupling of the two circuits.
E, high sensitive magnetic material wrapped wire, a magnetic field can effectively solve the interference problem is noteworthy that for forming the closed magnetic circuit and, in an effort to reduce the reluctance of the magnetic circuit will be more effective.
(2) high-frequency coupler, a high-frequency coupling means is longer than a 1/4 wavelength of the standing wave due to the trace voltage and current occurring in the circuit, will enhance the amount of coupling, can be employed to solve the following methods:
a, to minimize the ground line, and the housing ground as far as possible by way of surface contact.
B, refresh input and output lines of the filter, to prevent coupling between input and output lines to ensure that the filtering effect of the filter is not deteriorated.
c, shielded cable shielding multi-point grounding.
d, the floating connector pins to ground potential, which prevent the antenna effect.
3, to improve the system ground, the ground is preferably a zero impedance, zero potential physical entities, it is not only the reference point signal, the current flows and no voltage drop. In particular in electrical and electronic equipment, which does not exist over the ground, when a current flows through the ground would have a voltage drop. Accordingly base line can interfere with the formation mechanism can be attributed to the following two points:
First, to reduce the impedance and low impedance power feed.
Second, select the right mode and a barrier to the ground loop, to be divided by grounding suspension, a single point ground, multi-point grounding, the ground mixture. If the line is mainly sensitive to interference from external space or housing system, the suspension can be addressed at this time manner, but the suspension device prone to accumulation of static electricity, when the charge reaches a certain level, will generate an electrostatic discharge, the suspension should not be used to in general electronic equipment. Single-point ground circuit suitable for low frequency, current and frequency in order to prevent other stray current to generate a potential difference between the point of signal ground line, and signal ground and power ground isolation safety, the power cord is located in a large single point connection. Single-point ground is mainly applied to the frequencies below 3MHz. Multi-point grounding the high frequency signal is the only practical way to the ground, when the radio transmission line will exhibit characteristics such that the effectiveness of the multi-point grounding, when the ground conductor is longer than 1/8 wavelength of the highest frequency, require a multi-point grounding equipotential a ground plane. Multi-point grounding applies to 300KHz or more. Since the ground suitable for mixing have a high-frequency low-frequency electronic circuits.
4, the shield, the shield is an important measure to improve the electromagnetic compatibility of electronic systems and the electronic device can, it can effectively inhibit various electromagnetic interference propagating through space. Shielding mechanism can be divided by the electric field shield and the magnetic shield and electromagnetic shield. Electric field shielding should note the following:
a, selecting a material of high electrical conductivity, and should be grounded.
B, then choose the correct location and reasonable shape, preferably directly grounding shield. , Usually only the magnetic field shielding
Refers shielded DC or very low frequency magnetic field shielding effectiveness is far better than the electric field shielding and electromagnetic shielding, magnetic shielding is often the key projects, the magnetic shield when:
a, to choose ferromagnetic material.
B, the magnetic shield member away from the magnetic element, to prevent the magnetic short circuit.
c, the shield can be double or even triple-shielded.
d, the upper shield openings to be noted that the direction of opening, so that the long sides parallel to the slit as the magnetic flux flows, a minimum magnetic path length increases. In general, magnetic shielding is not required to ground, but in order to prevent the electric field sensor, or the ground as well. When the electromagnetic field by a metal or attenuation of electromagnetic field barrier, will be a certain degree of attenuation, i.e., the electromagnetic field shielding effect is generated. Depending on the specific needs of the actual rectification process may be selected and which shield shape, size, and the like grounding shield.
5, the wiring structure of the circuit board changes, some frequencies are distributed parameter line to go through the board determined, by the aforementioned method is not useful for such a small increase in the rectification by the trace inductance, capacitance, magnetic beads parameter changing circuit configuration, it moves to a higher limit frequencies required. For this type of interference, in order to solve it fundamentally affected, we must re-wiring.
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Original link: https://www.eeboard.com/news/emc/
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