On Thu, Aug 10, 2017 at 2:01 AM, mike.v...@gmail.com <mike.v...@gmail.com> wrote: > GND shielding parallel to the differentials is interrupted quite > often. Those GND tracks act as shields, for emission and reception. > I'd try to put as much parallel GND as possible. > > And trace the parallel GND around the via's, see attachment. > > Make sure the'res as much solid GND on the layer above and below the > traces, again shielding. > > Also I'd personally not use curved wriggles. HF signals travel in a > straight direction. With curves they start diffracting and start > bouncing cross each other and might start to radiate or echo back. But > I see that the community is divided on that stance.
I also prefer 45 degree corners to the curves. Looks like they only occur in one section. > If tight for space you can use 90% corners with a chamfered outer > edge. I suppose the chamfer acts like a mirror. > > https://www.maximintegrated.com/en/app-notes/index.mvp/id/5100 > Figure 6 This is good advice for single-ended signals on a stripline--high-speed digital and RF. That is the situation Maxim are addressing in the referenced document. The signals we are dealing with are high-speed digital but transmitted in differential mode on a microstrip. Single-ended signals are transmitted relative to a ground reference and so putting ground reference next to them tends to block the side-view of the antenna created by either microstrip or stripline, thus reducing radiated and coupled interference. That's a very good thing! microstrip (The following diagrams are in cross-section perpendicular to the direction of signal transmission. Think of the signal going into the diagram away from the viewer.) single-ended signal without ground shield traces signal + dielectric from the side we see a dipole antenna ground - single-ended signal with ground shield traces - + - ground signal ground - dielectric dielectrc dielectric ground ground ground ground - (ground shield traces would need some vias to connect them with ground plane) This blocks the view of the dipole antenna from the side and reduces the size of the dipole antenna so that far field it is vanishingly small being primarily the area between the ground shield traces and the signal trace. (Far field: distance from microstrip at least 10 * separation between signal and ground shield traces.) Since we have a different geometry, the problem changes. We are using differential microstrips. Differential-mode signals are transmitted relative to each other instead of ground. Only common-mode noise in the signals is transmitted relative to ground. microstrip differential-mode signal without ground shield traces signal+ signal- dielectric dielectric ground ground ground Here the dipole antenna is limited to area between the two signal traces, blocked on the bottom side by ground plane, and insignificant in far field (because the traces are close together, have opposite potential and currents, and the fields cancel each other). I'm out of time to add detail or references, so sending now. _______________________________________________ arm-netbook mailing list email@example.com http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to arm-netb...@files.phcomp.co.uk