It became a convention, and the PCB connected to various cables, in order to match the impedance, was finally required according to the 50-ohm impedance standard. Soon after, under the influence of the industry-dominant companies like Hewlett-Packard, the Europeans were forced to change, so 50 ohms eventually became a standard in the industry. At this time, the European standard was 60 ohms. After comprehensive consideration, it finally chose 50 ohms, and special ducts were manufactured and converted into The standard for a cable. An organization called JAN was established. 51.5 ohms are common, but the adapters/converters seen and used are 50 ohms to 51.5 ohms The Army and the Navy solved these problems. In the United States, the most used conduits are connected by existing gauges and water pipes. As technology advances, impedance criteria need to be given in order to strike a balance between economy and convenience.
In the early days of microwave applications, during the Second World War, the choice of impedance completely depended on the needs of use. We all know that a large part of modern electronic technology is derived from the military, and the military is slowly being converted to civilian use. I hope that more people can sum up more relevant factors from their respective perspectives.įirst of all, 50 ohms has a certain historical origin, which has to be said from the standard cable. High Speed also summed up the various replies to this question. Why are you saying that you are not good? The signal integrity problem itself is a trade-off problem, so the most famous sentence in the industry is: “It depends…” This is a question without a standard answer, and the benevolent sees the wise and sees wisdom. Different board materials, the dielectric layer thicknesses and constant (Dk), and the thickness of the metal traces all need to be part of the calculations. There are many factors that go into calculating the width of an impedance controlled trace. This means that the actual trace width for a 50 ohm line could vary from design to design. The most famous one is Howard Johnson, Ph.D.’s reply to this question, I believe many people have seen it. We also looked for a lot of information before writing this article.
Why do the common single-ended traces in the board default to 50 ohms instead of 40 ohms or 60 ohms? This is a seemingly simple but not easy answer. Many people who are just touching the impedance will have this question.