Why return path in PCB is as significant as signal path with an example

[sushl]

Hi
It would be Helpful if anyone can provide an example of why return path is significant in PCB design.

Thanks and Regards
Sush

[KlausST]

Hi,

do an internet search for:
"return path discontinuities"
"stripline return path"
"high speed layout guidelines"
and so on

...and you will find lots of documents, descriptions, tutorials ...

like this:
www.ti.com/lit/an/scaa082a/scaa082a.pdf

Klaus

[marce]

Its important because its 50% of the signal...

[dick_freebird]

Nothing happens until you close the current loop.
That is "the path". Not just the part you think is
"signal". The "signal" trace should be signal and nothing
but (in a perfect world). The return, that's a shared
resource unless you make it likewise clean and single
purpose.

Like, you may take a limo to the prom, but you are
going home on public transportation. So watch where
you sit, because that tux has a cleaning deposit.

[sushl]

Hi,

do an internet search for:
"return path discontinuities"
"stripline return path"
"high speed layout guidelines"
and so on

...and you will find lots of documents, descriptions, tutorials ...

like this:
www.ti.com/lit/an/scaa082a/scaa082a.pdf

Klaus

Thanks Klaus !!

I also have few Doubts while going through some PCB boards!!

What does loop inductance got to do with a transmission line!! Will they be resonant at Certain high Frequencies
say the charecteristic impedance of tx line is Z0= R+jwL so will equating the imaginary part to inductance give the value of Loop inductance?

Also what are stitching Via's purpose in pcb ?
searching on google said that stitching vias are used to eliminate the EMI on the signal traces. Apart from this is there any other reason.

when observing Pcb they have added vias around the the mounting holes can anyone give me an appropriate reason as to why this is done... ?


Thanks and Regards
sush