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I recently came across something odd to me recently. I’m working on test development for an Op-Amp that has a bandwidth of 800MHz to 1 GHz. It needs 50 ohm transmission lines of course, but there is a requirement for a capacitance of < 1pF on the inverting and non-inverting pins. This doesn’t make sense to me, is this even possible? Capacitance is required to make a transmission line.
Well, for there not to be any capacitance there would be impossible. If I remember correctly I think they mean “Excess” capacitance. It’s a warning not to have stubs or to run traces from that pin that are capacitive. There underlying problem isn’t the type that layouts typically have with capacitance. It has do with the leading and lagging of voltage versus current and that caps have the current leading the voltage, which results in throwing off the op-amp gain and related bad stuff. However, if you just avoid having any excess copper on that net you can keep it’s behavior inductive and should be okay.