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Topics - alm

1
Project development, ideas, and suggestions / Discussion: Effects of right-angel bends and propagation delay in microstrips
//EDIT by IPenguin// This thread has been split from the Logic Sniffer v1.03 manufacturing update thread.

The discussion started over a right-angel bend in one of the USB signal traces of the OLS v1.03 redesigns (between USB connector and MCU pad) and evolved into the rather general field of propagation of signals along traces on PCBs (in particular but not limited to microstrip on FR-4 expoxy), in particular the influence of right-angel bends on such signals in dependence on their frequency and rise/fall times (slope).

//END EDIT//

[quote author="rsdio"]
(*) On that note, the differential data traces look great on the v1rev3 PCB except for one thing: RC4/D- has a single right-angle turn in it which should probably be a couple of 45-degree turns like all the rest. Also, you might consider increasing the width of the D+,D- traces to be almost as wide as the PIC pads. It's actually difficult to know the impedance of the traces without coordination with the PCB fab house, but generally "wider" is better. My general rule is to go about as wide as the SMD pads and not worry about going beyond that.
[/quote]
Do you have any references about a measurable effect of right-angle bends on signals in the USB range? All papers I've found that actually did measurements considered the effects insignificant up to at least 4GHz or so, both impedance mismatch and EMI. Most of the arguments against right-angle bends seem to be based on belief, so I'd be happy with some hard facts. Of course it doesn't hurt to minimize these effects.