Electromagnetic and interference issues are almost a key factor in all PCB design, considering the problem of board layout phases to help mitigate many common problems. The noise generated by the power unit can reduce design performance and interfere with other equipment. The signal can interfere with each other and reduce system performance.
Understand how the system works, the nephew of the noise line position and the location of the low signal-to-than-sensitive line position helps optimize the board layout to avoid more problems in the design. To solve the EMI problem, the radiation can be blocked by adding a filter in a noise point or using a metal housing. However, these require a high cost, and the development process needs to continuously test and redesign the board, and time consuming. Since the key to EMI issues is edge effects and connector, the above redesign may even relate to mobile key I / O lines. In the early stage of the board design, the EMI effect is considered, and the quality of the final product can be greatly enhanced and any annoying trouble.
power supply
From the function to EMI and thermal characteristics, the board layout determines the success of each power project. The design switching power supply layout is simple, but it often appears in the later stage of the design process.
The good layout of the first prototype will not only increase cost, but in turn, in terms of EMI filters, mechanical masking, EMI test time and PCB operations can save a lot of resources. The radiation frequency of the switching power supply is more obvious, and it affects the nearby radio radio, but the good layout does not need to block such systems.
EMI problem is caused by rapid changes in current loop, so "heat loop" is avoided or ensured that it does not have a rapid change relationship throughout the design. Different power topologies (eg, a buck converter or reverse converter) produce different AC circuits, but it is properly arranged (sometimes within the circuit board), it is conducive to shielding all radiation effects, reducing the filter or Expensive metal housing needs. Make sure the above-mentioned loop away from the via and sensitive lines connected to different levels, which also help to reduce the impact of the power line on other systems.
Signal line
The maximum signal line is the noise generated by the I / O pin, which typically forms a large antenna. In synchronous design, all signals are switched in the same edge, which can periodically produce huge noise spikes. As the clock rate increases, the above signal is more important for board design.
Even if the parallel tracking of a short distance, it will accommodate string. The parallel distance, frequency, amplitude, and victim of the noise and the sound source voltage is proportional to the impedance of the victim.
By isolating the noise line with a more sensitive track, avoiding noise tracking outside the edge of the circuit board, can minimize it. At the same time, the noise tracking packet aggregate surrounds the ground line, which helps to reduce noise because all coupling are grounded, and is not connected to other signal lines. This is especially important for the I / O lines that generate noise and radiate the system.
The signal that may be a noise victim should be returned to the ground below. This reduces the impedance and reduces the noise voltage and any radiation range.
Clock tree
The oscillation circuit is the third noise source, and the oscillator is here for orbit. In addition to basic frequencies, the output also includes harmonics. Separation of crystals and other components and tracks of PCB, while maintaining a smaller ring regions typically avoid the above problems, and prevent signals from being coupled to other components (eg, large sensors).
Most EMI-related crosstalk occurs around the crystal, so the oscillator maintains at least 2 cm intervals to reduce any sensitivity. It is usually taken as part of the partition (as shown below).
Radiant antenna
A section of FM band radiant antenna is formed around 8 cm or longer. The above problems can be easily solved by avoiding longer signal lines and a series of resistors that provide damping, and it is easy to solve the above problems without lowering the data transmission speed. This is the location of the board layout feeds back to the network list during iteration.
The rushing line can also radiate from the corner, so the design tool rules should be labeled out of the rolling position. The above corners are also a manufacturing process to lead to risk factors that are generated, and therefore, the benefits of the above risk factors are avoided.
Partition
Create a similar functional partition, which helps to clarify the requirements of the board layout. Keep all analog components in the same area, shielded through the separation ground plane, specifically designed to protect partitions from power-driven grounding lines or digital circuitry, which can reduce the sensitivity to coupling noise. At the same time, for the design of the simulated area board, the digital components are weaker than the noise induction. Similarly, the power component is held in the same area of the circuit board, and it is also possible to stay away from other sensitive components.
Automatically select route
Automatically selecting routing tools seems to be very effective, taking into account the above factors and restricting tools. Automatic routing selection within the board partition helps to speed up the layout process while reducing EMI's impact on design. On the long signal line or noise signal line near the sensitive line (especially in I / O), it is difficult to implement automatic routing. Note that EMI's impact on these lines helps to promote automation design.
Tools such as DesignSpark PCB provide design rules to check, ensuring that the route is neither too close, and it will not be curved, but there is no great help for the EMI problem facing designers. Pay attention to sensitive lines, parallel signal tracking and long, seek ways to manually optimize these lines, signal captains, help significantly improve design quality and performance.
Summarize
EMI is a key design guideline, but only relying only on the automation location and line, the design rules of board layout may bring many follow-up problems. Pay attention to the EMI problem that the design is designed. Create an area that automatically selects the route, combining the value of the value of the automation design and the design expertise, which helps optimize the design, avoid board, additional filter, and even expensive housings. High cost redesign. The board is designed to consider EMI, which helps to produce the best product under the premise of saving cost and control time range.
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