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support@nextpcb.comHere you'll find insights into PCB design, tech trends, assembly issues, and trending topics
in the general news media as they relate to printed circuit board technology.
As experts in the manufacture and assembly of printed circuit boards, we work to make our blog a helpful resource on PCB topics and the industries that we work with, including automotive, consumer electronics, aerospace and many more.
In general, the most basic process of designing a board can be divided into three major steps.
In high-speed designs, the characteristic impedance of the controllable impedance plates and lines is one of the most important and common problems. First, let's look at the definition of a transmission line: a transmission line consists of two conductors of a certain length, one for transmitting signals and the other for receiving signals (remember that the "loop" replaces the concept of "ground"). In a multi-layer board, each line is part of the transmission line and the adjacent reference plane can be used as a second line or loop. The key to a line becoming a "perfect" transmission line is to keep its characteristic impedance constant throughout the line.
The main parasitic components generated by board layout are resistors, capacitors, and inductors. When switching from a circuit diagram to an actual board, all parasitic components have a chance to interfere with circuit performance. When a system mixes digital and analog components, careful routing is key to the success of the board. In particular, digital traces that are often close to high-impedance analog traces will cause severe coupling noise, which can only be avoided by keeping the two traces at a distance. This article quantifies the toughest board parasitic components, board capacitors, and lists the performance examples that can be clearly seen on the board.
PCB material are divided into: 94HB, fireproof board (94VO, FR-1, FR-2), semi-glass (22F, CEM-1, CEM-3), and full glass (FR-4).
Signal integrity issues can cause problems when you struggle to stabilize the various signals on the board. The IBIS model is an easy way to solve these problems. You can use the IBIS model to extract some important variables for signal integrity calculations and finding solutions for PCB design. The various values you extract from the IBIS model are an integral part of signal integrity design calculations.
4 methods and solutions
The PROTEL99 electrical layer is divided into two types, the positive layer and the negative layer. These two layers have completely different properties and usage methods.
The ways to control the effects of transmission line effects from the following aspects.
The PCB board is divided into many layers. What are the techniques for the high four-layer routing? Let me introduce you to the following.
Via is one of the important components of a multi-layer PCB. The cost of drilling is usually 30% to 40% of the cost of PCB board. Simply put, each hole in the PCB can be called a via.
The high-speed PCB layout technology driven by electrical rules realizes the design strategy of signal crosstalk control.
At present, electronic equipment is still used in printed circuit boards as the main assembly method for various electronic devices and systems. Practice has proved that even if the circuit schematic design is correct, improper design of the printed circuit board will also have an adverse effect on the reliability of electronic equipment. For example, if the two fine parallel lines of the printed board are in close proximity, a delay in the signal waveform is formed, and reflection noise is formed at the end of the transmission line. Therefore, when designing a printed circuit board, it should be noted that the correct method is used.
The abstract and complicated digital high-speed logic principle, how to transmit the square wave signal in the transmission line, and how to ensure its signal integrity (Signal Integrity), reduce the noise of its noise (Noise) and other professional expressions, if simple The example of life is explained, but instead of moving a bunch of mathematical formulas and difficult physics language, it is the inspiration and benefit for novices or interlocutors.
All of the examples in this article were developed using the multisim design environment, but the same concepts apply even with different eda tools.
Consider the power and ground planes
Printed circuit manufacturers want to use good dry film to ensure the quality of printed boards, stable production and improve efficiency. In recent years, with the rapid development of the electronics industry, the precision density of printed boards has been continuously improved. In order to meet the needs of printed board production, new dry film products have been introduced, and the performance and quality have been greatly improved and improved.
The current worldwide demand for environmental protection has made electronic products more demanding in the miniaturization of the Ministry of Energy. This has also spurred the advancement of high-speed and large-capacity electronic products for data and information processing. On the other hand, IT products that are personally demanded are also moving toward functional integration, high-performance (high-speed), and low-consumption power. In the signal transmission mode of electronic products, the parallel transmission mode develops toward a continuous mode. And the way in which optical transmissions have been added to electrical transmissions has begun to emerge. The high integration and high frequency development of electronic components has led to a continuous increase in the demand for high-frequency printed circuit boards.
The mechanical design includes selecting the appropriate board size, board thickness, board stacking, inner copper barrel, aspect ratio, and the like.
The application of differential signal in high-speed circuit design is more and more extensive. The most critical signal in the circuit always uses differential structure design. What other way is it so popular? How can we ensure good performance in PCB design? With these two questions, we will discuss the next section. What is a differential signal? In layman's terms, the driver sends two equal-valued, inverted signals. The receiver determines whether the logic state is "0" or "1" by comparing the difference between these two voltages. The pair of traces carrying the differential signal is called differential trace.
In circuit design, we are generally concerned about the quality of the signal, but sometimes we are often limited to the signal line for research, and the power and ground as the ideal situation to deal with, although this can simplify the problem, but in high-speed design This simplification is no longer feasible. Although the direct result of circuit design is manifested in signal integrity, we must not neglect the power integrity design. Because power integrity directly affects the signal integrity of the final PCB. Both power integrity and signal integrity are closely related, and in many cases, the main cause of signal distortion is the power system. For example, the ground bounce noise is too large, the design of the decoupling capacitor is not suitable, the loop effect is serious, the division of multiple power/ground planes is not good, the design of the ground layer is unreasonable, the current is not uniform, and the like.
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