磁珠与电感有什么区别?高频时磁珠怎么滤波?下文进行了很好解释!
电感是用来控制PCB内的EMI。对电感而言,它的感抗是和频率成正比的。这可以由公式:XL = 2πfL来说明,XL是感抗(单位是Ω)。例如:一个理想的10 mH电感,在10 kHz时,感抗是628Ω;在100 MHz时,增加到6.2 MΩ。因此在100 MHz时,此电感可以视为开路(open circuit)。在100 MHz时,若让一个讯号通过此电感,将会造成此讯号品质的下降(这是从时域来观察)。和电容一样,此电感的电气参数(线圈之间的寄生电容)限制了此电感只能在频率1 MHz以下工作。
问题是,在高频时,若不能使用电感,那要使用什么呢?答案是,应该使用「铁粉珠(ferrite bead)」。铁粉材料是铁镁或铁镍合金,这些材料具有高的导磁系数(permeability),在高频和高阻抗下,电感内线圈之间的电容值会最小。铁粉珠通常只适用于高频电路,因为在低频时,它们基本上是保有电感的完整特性(包含有电阻和抗性分量),因此会造成线路上的些微损失。在高频时,它基本上只具有抗性分量(jωL),并且抗性分量会随着频率上升而增加。实际上,铁粉珠是射频能量的高频衰减器。
其实,可以将铁粉珠视为一个电阻并联一个电感。在低频时,电阻被电感「短路」,电流流往电感;在高频时,电感的高感抗迫使电流流向电阻。
本质上,铁粉珠是一种「耗散装置(dissipative device)」,它会将高频能量转换成热能。因此,在效能上,它只能被当成电阻来解释,而不是电感。
用户1161998 2007-4-2 10:26
second part
No business travel here – strictly pleasure, the only reason to fly. My wife turns off her virtual Sudoku. Did I leave the stove on, she asks. Some things never change. I access my home monitor and confirm that she did, indeed, leave it on. I turn it off and check that my security systems are functioning properly. The cameras know when to alert me of anything strange and are also programmed to recognize my friends and family – which is good because my daughter is picking up my social security check ¬apparently the only piece of mail I still receive. You see, my wife made me retire again!
The airport is crowded but moves as quickly as the traffic. It takes one minute to get through security as my implanted information and my person are scanned. I lose my wife to one of the gift shops and quickly check her GPS position. She’s buying the latest e-book and with a scan of her ID chip, we’re on our way. In two hours we’ll be in Rome, just enough time for a short nap for this tired digital self.
This vision for the next twenty-five years is profound, but also raises challenges. To bring portability, connectivity and intelligence to every electronic device, semiconductor companies will need to hide the inherent complexity of creating such devices. Complete system solutions consisting of hardware, software and tools that spawn cooperative signal processing will be of paramount importance. With its expertise, technology and industry collaboration, TI is poised to address these challenges just as it has consistently conquered performance, price and power obstacles.
We are at a thrilling time in history, and life as we know it is about to change. It’s already happening – we will make it happen together.
If you have a vision of what the future will hold, send it to me. Put yourself in 2020 and imagine where DSP technology will take you.
用户1194378 2006-9-16 20:52
很明确的解释,我原来都不明白什么是磁珠,后来电路里看到过,但是不是很明白她的用途。谢谢