<dos1>
I'll try to take a look at what's wrong with the neo900.org repo, but not sure yet when
<houkime>
a bit sad that my branch is actually the most recent.
<houkime>
nobody worked on neo900 after me it seems.
<houkime>
(in ee-full i mean)
<norly>
thanks guys
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<houkime>
trying to figure out where to best place a common mode choke on a differential pair which then goes through a connector and through a cable
<houkime>
and fo 500 MHz (Neo900/N900 CSI) I can't really think of a way the exact placement could make a significant difference
<houkime>
Joerg-Neo900, do you know of any particular design considerations for that? I searched for several hours today and learned a lot of new things about differential pairs but couldn't really find an answer for placement of common node chokes.
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<houkime>
*mode chokes.
<houkime>
STI filters application notes for example just say to place them on the both sides of the cable somewhere between a connector and an IC but that's it.
<houkime>
physics-wise, 500 Mhz has a wavelength of 60 cm and even if we consider an edge to be 10-20 cm it is very huge.
<houkime>
that said, noise can have a higher frequency than 500 MHz
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<houkime>
DocScrutinizer05, ^^^^
<DocScrutinizer05>
depends on particular design
<DocScrutinizer05>
There must be the repos which our last layouter created
<houkime>
DocScrutinizer05, I am speaking about a connection between neo900 front camera (via display connector) and bb-xm
<DocScrutinizer05>
hmmm
<houkime>
it wasn't layed out unfortunately neither by me or by metacollin
<DocScrutinizer05>
get a plain ferrite block / bead and place it on top of the diff pair, find the place that works best
<DocScrutinizer05>
for better effect, shield the diff pair with a plane above and below
<houkime>
DocScrutinizer05, the schematics specifies the exact part number for a choke. ACM2012H. It was actually the placement i was not sure about.
<houkime>
As far as physics and documents i found go, the difference between places should be quite negligible.
<houkime>
at least on +- a few cm scale.
<Joerg-Neo900>
check N900
<Joerg-Neo900>
I guess it's legacy
<houkime>
Joerg-Neo900, thanks. Haven't though about just checking original pcb.
<houkime>
*thought
<Joerg-Neo900>
the purpose is to block common mode signals from reaching chip inputs. Noixe gets picked up on long traces
<houkime>
Joerg-Neo900, from this logic the ideal placement is near client ICs on both sides. Thoughin this particular case both clients are not on neo900 (one on bb-xm and one on front panel near display)
<houkime>
and in schematics there is only one CMF per differential lane and not 2.
<houkime>
the question is then - does N900 frontal camera has a CMF of its own?
<houkime>
if it does and if there is also a CMF on bb-xm then CMF on neo900 itself shouldn't be needed.
<houkime>
however, i doubt that any of the ends actually has CMFs
<houkime>
pins on bb-xm connector which are carrying differential signals for CSI were chosen on an unclear principle.
<DocScrutinizer05>
only one needed when signal direction unidir
<DocScrutinizer05>
the pins prolly where chosen for their function
<houkime>
which is... based on bb-xm docs, DVI? And also one stray pin which is on another connector entirely.
<houkime>
though there might be some multiplexor magic going on...
<houkime>
however mux magic is unlikely to create and destroy CMFs on bb-xm.
<houkime>
So, if unidir, then logically CMF should be near a receiver.
<houkime>
And there are 2 data lanes in CSI.
<houkime>
I don't however know how exactly they are directed.
<houkime>
they might be both from camera to bb-xm, or one to camera and one to bb=xm
<houkime>
clock-wise, one can suppose that bb-xm is master.
<houkime>
so for clock lane camera is a receiver.
<houkime>
however, in the first scenario where camera has 2 lines to bb-xm it becomes uncontrollable and can operate only in some default mode.
<houkime>
hmm... or not if not only CSI is present. need to check.
<houkime>
it seems like there is only CSI, one extra external clock signal (for some reason), 2 powerlines and a shutdown signal.
<houkime>
found the front camera model ST Microelectronics VS6555.
<houkime>
aaand it has nothing to do with csi whatsoever. It uses some cryptic CCP 2.- for data which is one clock diff. lane and one data lane.
<houkime>
*CCP2.0
<houkime>
CCI which is used for commands is 1 data pin and one clock pin. And that's it.
<houkime>
Perhaps ccp was wrongly identified as CSI on the display connector, but then there is a question: for whom is the second dataline and if it even exists.
<houkime>
Joerg-Neo900, i couldn't find based in what data the pinout of the neo900 display connector was established.
<houkime>
*based on what data
<houkime>
i found in neo900 feasibility study that "cdp" interface is used by the panel also. (2 lanes + SPI)
<DocScrutinizer05>
I think this is covered in out proto-v2 whitepaper. Or ask wpwrak
<houkime>
DocScrutinizer05, v2 says nothing about front camera, i checked
<DocScrutinizer05>
I'm really sorry I tried to keeep ALL this in my mind for over 5 yeras. At one point in time some headcrash and trash collection happened
<DocScrutinizer05>
Neo900 mimics a N900, so the pins on BB-xM are same as on N900
<DocScrutinizer05>
and yes, I think this is covered in v2 whitepaper
<DocScrutinizer05>
more generically as I just paraphrased
<houkime>
I have checked original N900 board. All 3 CMFs are grouped right near display connector. However it doesn't seem to have any ESD protection which neo900 schematic calls for.
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