I. Anti-interference and electromagnetic compatibility
The defined interference of the interference means the disturbance of the liquid crystal module caused by external noise and unwanted electromagnetic waves in the reception. It is also defined that, upon receiving some of the desired signals, the disturbing effects caused by the undesired energy, including the effects of other signals, spurious emissions, human noise, etc., are typically not calculated from the noise.
Electromagnetic compatibility and anti-interference electrical equipment and electronic circuits are subject to external interference on the one hand, and on the other hand, it will interfere with the outside world. The electronic signal is a useful signal to the circuit and may be noise to other circuits. The anti-interference technology of electronic circuit is an important part of emc. Emc is the abbreviation of electro-mag-netic compatibility and is translated into electromagnetic compatibility. Electromagnetic compatibility is a function of an electronic device that can perform its functions in an electromagnetic environment without generating intolerable interference. The electromagnetic compatibility has three layers:1. The electronic equipment shall have the ability to suppress external electromagnetic interference;2. The electromagnetic interference generated by the equipment itself shall be lower than the specified limit and shall not affect the normal operation of other electronic equipment in the same electromagnetic environment; The electromagnetic compatibility of any electronic equipment is measurable
II. The anti-interference three-element electromagnetic interference must have three elements at the same time: the electromagnetic disturbance source, the coupling way of the electromagnetic disturbance, the sensitive provision and the circuit of the electromagnetic disturbance. 1. The source of electromagnetic disturbance includes the source of natural disturbance and the source of human disturbance. 2. The coupling method of electromagnetic disturbance includes two kinds of coupling between conduction and convergence. (1) conducting coupling: the noise is connected between the disturbance source and the sensitive equipment, and is conducted from the disturbance source to the sensitive equipment, the electric circuit and the interference phenomenon. The transmission circuit comprises a wire, a conductive part of the device, a power supply power supply, a common impedance, a ground plane, a resistor, a capacitor, an inductance and a mutual inductance element, and the like. (2) radiation coupling: the disturbance signal propagates in the form of a radiation electromagnetic wave through the medium, and the disturbance energy is emitted in the space around the electromagnetic propagation law. There are three common types of radiation coupling:1. The electromagnetic wave transmitted by the harassing source antenna is accidentally received by the antenna of the sensitive device, referred to as the coupling of the antenna to the antenna;2. The spatial electromagnetic field is inductively coupled via a wire, referred to as a field-to-line coupling;3. High-frequency signal induced production coupling between two parallel conductors is called line-to-line coupling. The conductive coupling includes an inductive and capacitive coupling between the conductive coupling and the wire. The radiation coupling includes near-field coupling and far-field coupling. 3. Sensitive equipment and circuit for electromagnetic disturbance: all low-voltage and small-signal equipment and circuits are sensitive equipment and circuits for electromagnetic disturbance. 4. The anti-interference three-element formula describes the degree of interference of a circuit. If n is used, n can be used to define the n = g * c/ i formula: g is the intensity of the noise source; c is the coupling factor of the noise source through some way to the interfered; i is the anti-interference performance of the interfered circuit. G, c, i are three elements of anti-interference. As can be seen from the formula, the degree of interference of one circuit is proportional to the intensity g of the noise generating source, in proportion to the noise coupling factor c, inversely proportional to the interference resistance i of the interfered circuit. To make n small, you can use the following method:1. G is small, that is, the intensity of the existing interference source is suppressed to be small at the occurrence of the interference. 2. C To be small, the noise is attenuated very much in the propagation path. 3. I increase, to take anti-interference measures at the affected part, to improve the anti-interference ability of the circuit, or to suppress the noise at the disturbed place. In practice, different measures shall be taken in accordance with the conditions. Some measures can be taken only from one side, and there are three aspects that can be taken. The theoretical analysis and engineering practice have proved that the suppression of noise at the noise source is the most effective anti-interference. The anti-interference (electromagnetic compatibility) design should be based on the three factors, so that the interference can be suppressed, and the electromagnetic compatibility standard is achieved, namely, the disturbance source is restrained, the coupling electric path is cut off, and the immunity of the sensitive equipment is improved. III. The principle of finding the noise source is complicated, and the method of suppressing the noise at the noise source should be first studied. The primary condition is to find the interference source, and then to analyze the possibility of suppressing noise and taking corresponding measures. There are obvious sources of interference, such as lightning, radio transmission, operation of high-power equipment on the power grid, etc. This interference source cannot take measures at the source of interference.