1. anti-interference and electromagnetic compatibility
1. Definition of interference
Interference refers to the disturbance caused by external noise and useless electromagnetic wave in the receiving of liquid crystal module. It can also be defined as the disturbance effect caused by unneeded energy, including the influence of other signals, spurious emission, artificial noise, etc. .
２. Electromagnetic compatibility and anti-interference
On the one hand, electrical equipment and electronic circuits by external interference, on the other hand, it will produce interference to the outside world. Therefore, the electronic signal is a useful signal to the circuit, and other circuits may become noise.
The anti-interference technology of electronic circuit is an important part of EMC. EMC stands for e lectro MAG something netic Compatibility, which translates as electromagnetic Compatibility. Electromagnetic compatibility is a function of electronic devices that perform their functions in an electromagnetic environment without causing intolerable interference.
The Electromagnetic compatibility has three meanings: 1. Electronic equipment shall be capable of suppressing external electromagnetic interference. 2. The electromagnetic interference generated by the equipment itself shall be less than the prescribed limit and shall not affect the normal operation of other electronic equipment in the same electromagnetic environment; 3. The Electromagnetic compatibility of any electronic device is measurable.
Three elements of anti-interference
There are three elements to constitute electromagnetic interference: source of electromagnetic interference, coupling way of electromagnetic interference, sensitive equipment and circuit.
1. Electromagnetic disturbance sources include natural disturbance sources and man-made disturbance sources.
2. The coupling ways of electromagnetic disturbance include conduction and radiation.
(1) conduction coupling: It is the interference phenomenon that the noise is conducted and coupled from the disturbance source to the sensitive equipment and circuit through the connection between the disturbance source and the sensitive equipment. The transmission circuit includes conductors, conductive parts of the equipment, power supply, common impedance, ground plane, resistors, capacitors, inductors and mutual inductors, etc. .
(2) radiation coupling: The disturbance signal propagates through the medium in the form of radiated electromagnetic wave, and the disturbance energy is emitted in the surrounding space according to the law of electromagnetic propagation. There are three common types of radiative coupling: 1. The electromagnetic wave emitted by the disturbance source antenna is accidentally received by the antenna of the sensitive equipment.2. The space electromagnetic field is inductively coupled by a conductor, which is called field-to-line coupling.3. The high frequency signal induction production coupling between two parallel conductors is called line-to-line coupling.
4. Anti-interference three-factor formula
describes a circuit by the degree of interference expressed in N, then n can be used to define the N G * C / I formula: G as the intensity of the noise source; C is the coupling factor that the noise source transmits to the disturbed place through some way; I is the anti-interference performance of the disturbed circuit.
G, C, I that means anti-interference three elements. It can be seen that the degree of interference in a circuit is proportional to the intensity g of the noise source, proportional to the coupling factor C, and inversely proportional to the anti-interference performance I of the disturbed circuit. To make n smaller, you can do the following:
1. G to be small, that is, the objective existence of the interference source intensity in place to suppress small.
2. C should be small, the noise in the transmission path to give a great attenuation.
3. I increases, in the interference place to take anti-interference measures, so that the anti-interference ability of the circuit, or noise suppression in the interference place.
The design of anti-interference (EMC) should start from three factors to restrain the interference and reach the EMC standard, that is, to restrain the source of disturbance, to cut off the coupling electric way and to improve the immunity of sensitive equipment.
3. The principle of searching for noise sources,
no matter how complex the situation, should first study the method of suppressing noise at the noise source. The first condition is to find the interference source, the second is to analyze the possibility of suppressing noise and taking corresponding measures.
Some interference sources are obvious, such as lightning, radio transmission, power grid on the operation of high-power equipment. This interference source can not take action at the source of the interference.
Electronic circuits are more difficult to find sources of interference. Find the source of interference is: current, voltage changes dramatically is the place of electronic circuit interference source. In mathematical terms, the large areas of DI / dt And du / DT are the sources of interference.
4. Principles for finding the means of noise propagation
1. The main source of inductive coupling noise is usually the case of large current variation or large current operation.
2. Voltage variations are large or high in the case of high-voltage operation, usually the main source of capacitive coupling.
3. The noise of the common impedance coupling is also caused by the voltage drop on the common impedance due to the drastic changes in the current.
4. For the drastic changes in the current, its inductance component caused by the impact is very serious. If the current doesn’t change,. Even if their absolute value is very large, they do not cause inductive or capacitive coupling noise and add only a steady voltage drop to the common impedance.
Three elements of anti-interference
Post time: Jun-09-2020