Part of the conceptual difficulty here is that network theory can't tackle these issues very well. To really understand circuits you need to use physical optics: a circuit board is a collection of coupled waveguides. Network theory is the long wavelength limit of physical optics, but the trouble arises when the relevant wavelengths aren't so long.
I'm always amused by the notion of "voltage noise on ground". Relative to what? Sound of one hand clapping. Voltages are relative. Where is the electromagnetic noise field coming from, and how is it coupled to the port you want it to stay away from? Do you guide it away by configuring conductors? Better understand the leaks in your waveguide. Do you reflect it away with reactive components? Where does that unwanted energy go? Is there another reflector that just sends it back? Or do you try to absorb it? Decoupling resistors and lossy ferrites are the RF equivalent of black paint... Inductance of capacitors? Magnetically, a capacitor is pretty close to a slug of metal of the same shape. It's not meaningful to quote an inductance for such a thing by itself: the return circuit has a great deal to say about that. Formally, the inductance per unit length of a straight conductor with magnetic field extending to infinity is infinite: the return circuit causes the field to fall off more rapidly and the inductance to converge. But that means that the test fixture is at least as important as the capacitor itself in determining the inductance: where does the return current flow? One strange assertion I've recently heard is that one should avoid high K ceramics for bypassing, because their dielectric absorption raises their impedance. I don't buy it: I've never seen dielectric absorption (either on a data sheet or in a circuit) so bad it dominated the impedance, so a larger value high K capacitor is going to have lower impedance than a smaller value low K capacitor. For equal value, yes, the high K capacitor's impedance will be a little higher, but the point of going to high K is usually to get more capacitance. John Doty Noqsi Aerospace, Ltd. http://www.noqsi.com/ j...@noqsi.com _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user