Gregory's Server
@tubetime I honestly think this is ill-advised, because it makes the very signal lines whose signal we did this whole connection for cross reference levels and hence become noisy at the receiver. That's not really an option for single- ended signals, and the differential ones you would encounter today would be very unhappy about the break in impedance and the complete loss of current return path (much more energy in the E-field between diff traces and their joint adjacent ground plane than …
|
3 comments
@tubetime @funkylab I think you’re right. Just remember that “low frequency” that does cross the ground plane better have very slow rise/fall times. I could not find the >1GHz EMI that was radiating from my board. Long story short, it was a 32kHz oscillator with a 800fs rise/fall time. In the oscillator manufacturers defense, the datasheet only had a maximum rise time spec. But who would have thought the edges would be that sharp!  @MarkAtMicrochip @funkylab you can sorta cheat a bit with high slew rate signals if they have a very long period and if you quasipeak during the EMI scan, but yeah usually high slew rate signals are a problem. |
@funkylab yeah the book advises building a ground "bridge" directly underneath high speed traces that cross over. they have high frequency return currents that take the path of least inductance (directly underneath) and if you have a ground cut underneath then the loop area increases, and you start radiating...