The source of interference suppression is to reduce the interference source du/dt, di/dt as much as possible. This is the highest priority and the most important principle in anti-jamming design, and it will often have a multiplier effect. Reducing the interference source du/dt is mainly achieved by connecting capacitors across the interference source. Reducing the interference source has a very important effect on high-speed circuits. Let's take a look at how to minimize EMI at the source. First, cut off the spread of interference According to the interference propagation path can be divided into two types of conductive interference and radiation interference. The so-called conducted interference refers to the interference transmitted to the sensitive device through the wire. Different frequency bands of high-frequency interference noise and useful signals can be cut off by the method of adding filters on the wires to cut off the propagation of high-frequency interference noise. Sometimes, it can also be solved by adding an isolated optocoupler. Power supply noise is the most harmful and special attention must be paid to handling. The so-called radiated interference refers to interference that propagates through spatial radiation to sensitive devices. The general solution is to increase the distance between the source of interference and the sensitive device, isolate them with ground and add a shield on the sensitive device. Second, shielding interference (1) In general, in the PCB design, we usually use high-current switching lines. On both sides of high-frequency lines, ground lines should be used to shield electromagnetic interference emissions. Also used to shield external noise from data lines (2) The use of shield isolation allows external electromagnetic waves and internal electromagnetic waves such as components, circuits, or systems to absorb energy (eddy current loss), reflect energy (interface reflection of electromagnetic waves on the shield), and cancel energy (electricity) The magnetic induction produces a back electromagnetic field on the shielding layer, which can cancel out some of the interference electromagnetic waves, so the shielding body has the function of weakening the interference. When the frequency of the interfering electromagnetic field is high, the eddy current generated in the low-resistivity metal material is used to form the offset effect of the external electromagnetic wave so as to achieve the shielding effect. When the frequency of interfering electromagnetic waves is low, high permeability materials should be used so that the lines of force are confined within the shield to prevent diffusion into the shielded space. In some cases, if a good shielding effect is required for both high-frequency and low-frequency electromagnetic fields, different metal materials are often used to form a multi-layer shield. (3) conductive paint. EMI conductive paint spraying technology has high conductivity, high electromagnetic shielding efficiency, spraying operation is simple (same as surface painting operations, only need to spray a thin layer of conductive paint in the plastic shell) and other characteristics, widely used EMI shielding for electronic products such as communication products (mobile phones), computers (notebooks), portable electronic products, consumer electronics, network hardware (servers, etc.), medical instruments, home electronics products, and aerospace and defense. Applicable to a variety of plastic shielding (PC, PC + ABS, ABS, etc.). The spraying of conductive paint solves the limitation of space limitation, operation, and cost pressure due to the metal shield. Because the conductive paint spraying operation is extremely simple, the metallization of the plastic is achieved. Third, eliminate interference (1) Optimize circuit design Increase filter circuit, anti-interference circuit and power supply decoupling circuit. These circuits are in principle simple and practical, because adding more complicated circuits will not only increase the material cost, but will also reduce the reliability of the product, and at the same time may cause new interference. In situations where some ICs are sensitive to power supply noise, four capacitors and an isolation inductor can also be used to ensure that all noise is filtered out. The choice of the size of the four capacitors is based on the frequency range of the interfering signal and its own harmonic frequency and its pin inductance. The corresponding capacitance is smaller The capacitor filters out higher frequency interference, and the corresponding capacitor with larger capacitance is suitable for filtering out lower frequency noise signals. Inductor L can't couple high-frequency noise from the power supply to the chip, usually About 10μH color ring inductance, and the order of these capacitors should be: The smaller the capacitance, the closer to the IC pin. (2) In order to eliminate the RF current in the PCB, magnetic flux elimination or flux minimization is a relatively common concept. Because the magnetic flux lines run in the opposite direction of the transmission line, if we make the RF return path, parallel and adjacent to the source, the magnetic flux lines in the return path (field in the opposite clock direction), and source The end paths (fields clockwise) are compared and their directions are reversed. When we combine the clockwise field and the counterclockwise field with each other, the cancellation effect can be produced. If unnecessary flux lines can be eliminated or minimized between the source and return paths, then radiated or conducted RF current will not exist unless on the minimum boundary of the trace. The main techniques for eliminating magnetic flux are: 1 Capture the magnetic flux lines generated inside the plastic package of the assembly to the 0V reference system to reduce the amount of radiation emitted by the assembly. 2 Choose logic components with caution and minimize the amount of RF spectrum radiated by components and traces. Devices with slower edge rate can be used. 3 Reduce RF currents on-line by reducing the RF drive voltage. 4 Reduce the ground noise voltage, which exists in the power and ground plane structures. 5 When it is necessary to push the maximum capacitive load, and the pin positions of all devices are switched at the same time, the decoupling circuit of the device must be sufficient. 6 The frequency and signal traces must be properly terminated to avoid ringing, overshoot, and undershoot. 7 Wrap the clock trace around the return path to the ground plane (multi-layer PCB), ground grid, and use the ground traces, or safety traces, for the single-sided and double-sided boards. Trace). Optical Rotary Sensor,Custom Encoder,Optical Encoder 6Mm Shaft,Handwheel Pulse Generator Jilin Lander Intelligent Technology Co., Ltd , https://www.jilinlandermotor.com