![]() In the past, researchers have had trouble creating intelligent robots that replicate cutting. Nanotechnology and the concept of friction.Nanotechnology Examples and Applications.The best trial offers and discounts for students.How to become a science blogger and set up a science news site in 4 steps. ![]() A Guide to Funding Nanotechnology Ventures.10 Things You Should Know About Nanotechnology.Nanotechnology Companies & Laboratories.Subscribe to one of our Daily Newsletters.So their requirements led to a circuit to solve a problem they would otherwise have. They prevent particularly high frequency switching noise from the PLLs reaching board supply rail tracks and planes and radiating EMI. Those analogue circuits have particular requirements and these extra filters as a result. I imagine you have seen ferrite beads used in the supplies of PLLs within FPGAs. Their manufacturers nearly always specify minimum power supply decoupling capacitance, sufficient to reduce supply noise from typical switching supplies to suitable levels. So, taking your question to the correct starting point: do FPGA supply rails require any additional filtering, such as by series ferrite beads? Although this can be counterbalanced by decoupling capacitors, it shows that inductors are to be used with care. A complex logic load like an FPGA draws high spike currents when its push-pull logic circuits transition, so when they demand current then the series inductor will obstruct it and the load voltage will fall, creating the noise they were there to magically stop. Inductors present a high impedance in response to a current change. Inductors are sometimes wrongly regarded as 'magic frequency stoppers'. Inductors can be used in power supply filter circuits to remove high frequency switching noise from reaching the load. Inductors have performance characteristics that can be used to perform functions required by a circuit, once a requirement has been identified. So every part must earn its keep and be justified. The latter has a cost, an effect on reliability and consequences from sourcing and obsolescence. The solution may be to do nothing or to do something. ![]() This may be a problem with my particular browser brand and version.Īs with all engineering, a problem is observed and quantified and a commensurate solution implemented. The previous version of the tool used to show this nicely. To learn more about the topic, I highly recommend an encyclopaedic appnote by Murata, numbered C39E - if I should recommend specific pages, check out page 24 in the file (20 in print) and for a complex view, read the whole chapter 8 starting on page 68 (64).Īlso, for a basic idea what anti-resonance does, I'd recommend an online tool by Kemet, called the KSIM - unfortunately, for some reason, the recently introduced v3 of the KSIM doesn't allow me to select the "combined" curve of ESR+Inductance, which is where the anti-resonant peaking is supposed to emerge. And, the fastest chips need to have some blocking in the package or on chip = any filter designed by you on the board around the chips can only do so much (some distance will always be left between your fastest ceramic cap and the package / chip). There are special low-ESL capacitors specifically designed for power blocking. You don't even need to add an explicit inductor of your own -) If you do need an inductor, you might want to consider throwing in some resistors too, to muffle the Q of the various resonant poles. And, when you combine several of them, you get anti-resonant behavior. So in that context: be aware that even SMD ceramic capacitors have an inherent resonant frequency. If I should understand your question in a broader context, you are asking about proper power blocking for fast digital chips. I've done some hands-on with LC filtering of power for a multi-stage RF amp cascade (a DIY noise generator, with several stages of SiGe amplification) and my initial designs have quickly explained to me that inductors and capacitors combined result in marvellous resonant peaks and nulls. If you use a choke as part of a filter, you'd better have a good idea how that filter behaves, as a whole :-) Try simulating the filter in Qucs/QucsStudio for a start, and be aware that the simulation will probably omit some painful real-world parasitic properties of the components and the PCB. A choke in series with the supply rail is no silver bullet.
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