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[Music]
he so uh welcome our next speaker
Equinox just take it away uh yeah hi
everyone I'm
equi um if you've looked at the far plan
schedule uh this is unfortunately a b
little bit of a rescue effort because I
had a hardw problem yesterday so I had
to recreate the entire presentation uh I
apologize ahead of time for this being a
little bit less uh polished that I would
have liked um it to be um
so let's start with a quick outline of
what I want to talk about here um I hope
you did look at the talk description if
you don't know where you are then maybe
go figure that out um
the this is mostly about how to do HF
design without knowing how to do HF
design um it's a bit of a experience
report from having it
done um I'm first going to give some
general framing so you know what the
goal is what the target is um I'm going
to go talk about a little bit about why
this is
generally something people
don't like doing why it's hard
um how I ended up doing it without
having the proper tools for it what the
result was um and then there's some room
for General things about uh this thing
um I am a software person um I don't
build Hardware as a job I never learned
how to build Hardware
um I pick up things um if you talk to
someone who knows uh how to do HF design
uh raise your hand if you actually know
how to do HF design with like oh there's
someone here in the video team um one
more you you will be incredibly bored
and if you see some me saying something
that is wrong feel free to correct me um
okay um also if you talk to someone
afterwards and they tell you
I said something that was completely
wrong that is very easily
possible um this got started as um a
project from the CCC no um from running
event
networks um if you have been around for
29 C3 till 33 C3 uh when we were in
Hamburg the building has a lot of shitty
fiber um and
um yeah it it wasn't great and um to
deal with that um the idea uh was to go
look at maybe making some tool for for
helping with that um in the particular
case of the
CCH the problem is actually dispersion
which if you have multimode fiber the
signal has multiple modes that's the
definition of a multim mode fiber that
can take and those have different speeds
so the signal gets mus mushy kind of I
don't have an insallation of this but we
we can talk about this later in the talk
it's coming going to come up again so
the idea was born to make a kind of a
fiber tool for building networks for
debugging
networks um originally just to extend
Connections in the CCH when we were
range limited um this kind of evolved
into a more generic multi-tool
later
um if you work with network equipment
and homebuild tools in this area you may
know that there are some pcbs that
connect to um fiber transceivers just
directed to each other um this was not
the goal here uh the goal was to have an
active repeater
um I'm noticing a few confused faces uh
I think I will go a little bit further
in explaining what the the goal here is
um I didn't include slides for this uh
actually the next slide is good for this
um this is the the Prototype of of this
project what you can see on the left
those two metal cages with numbers one
and two um those are slots for optical
transceivers for running network over
fiber um you put a module into that that
matches the infrastructure that you need
for your network that might be a multim
mode transceiver a single mode
transceiver a single mode transceiver
with very long range depending on what
your cabling is um if you have a
InterContinental fiber going through the
ocean you may want to use a very
longrange transceiver and some
amplifiers in the middle it's it's made
into separate modules so you can adapt
to the situation that you have at hand
you use the transceiver that you need um
those run at 1 gbit 10 g gabit 25
gigabit soon even more uh 25 is the
current limit for this form factor um
but this talk is about 10 gab ethernet
mostly um which was current at the time
that this I I started this project
um this thing has I've built this like
four years ago it was just an attempt at
getting something going um you can see
there's a small little
chip uh right immediately to the right
of those two slots um and that is an
active electrical repeater um let's go
back to the previous slide for a little
bit um you can frequently find these
boards without that chip in there which
means the two transceivers that you have
for converting your fiber signal uh into
the interface that you're system needs
they are just connected back to back to
each other so the output from one goes
into the input from another that in this
case was EXA was specifically a
requirement that this is not enough
because in a situation like in Hamburg
with the building with the shitty fibers
you get a shitty signal and just
retransmitting this shitty signal is not
going to help you so I I I hope I
collected some more people to see where
where this is
going um as I said this is the first
prototype um it did actually
work um this is the current version um
the slide is mostly here so you know
what I'm actually talking about in the
next slides um the actual problem here
is there's a lot of high-speed signals
four in this case coming from four
receivers um and you need to deliver
those and um dealing with in this case
five gigahertz of an electrical signal
is not a lot of fun um so let's get into
the
actual topic of this uh
presentation um it's not easy to do
these designs um the handbook for this
this is one of the references that
people point at when you try to get
started in this general area it's it's
literally called a handbook of black
magic um and it is appropriately called
that
um as soon as your signals start to get
a little bit faster um you don't
actually have like rectangular waveforms
anymore for your signals everything
starts to get
mushy um and this is the first
recommendation basically that I would
that I have buried in this talk um this
book is still relevant um the physics
doesn't really change the chips have
gotten a lot better um and there is
basically with chips getting better they
also get better at dealing with 3D
signals they get better at outputting
clean signals so you can just multiply
everything in this book by some factor
and it still applies it's just if this
book says something about 10 MHz it
might now apply for a higher frequency
in some cases because the the the
Silicon has just gotten better this
doesn't apply everywhere but it applies
somewhere this book is also great to get
started to understand what you don't
understand so I coming from a position
of knowing exactly nothing about this um
this book for me was a good point of
entry to figure out oh this will be a
problem that will be a problem that will
be a problem um let's look at actual
high frequency electronics and
considerations in this area um you start
from your naive Assumption of having an
ideal cable which is just a
wire um that works I don't know maybe
maybe to the megaherz range I think even
in in the higher me range you get
problems with this when when you start
getting problems you start considering
the cable as as a sequence of parasitic
elements they're called parasitic
because they're not intended to be there
so what you see at the bottom here is
just a model of what you treat the the
cable like um suddenly you have
capacitance you have resistance you have
inductive elements um the the cable
isn't built like this this is just a
model of understanding what the cable
does but this is only the first level as
soon as you start going into even higher
frequencies um in this case this is a
vertical cut simulated through a printed
circuit board um with two signals and
you can see on the right hand side uh is
the energy
distribution um of the signal being
propagated along the the the the trace
on the PCB and you can see it's not
actually uniform in the trace anymore
the trace is black all the energy is
Flowing on the outside of the
trace um so you you really can't
consider a wire or a trace wire anymore
it it behaves in in odd ways
um when you go to higher frequencies
again um you should be simulating your
design in some software that just takes
a 3D model of your entire uh printed
circuit board and
um divides it into very tiny elements
and just calculates uh Maxwell's
equations for every single element um
and by doing that you can get a better
impression of what your printed circuit
board actually behaves like when you put
a signal on it um this currently I'm not
sure how far the key cat support for
this has come um when I started the the
project there was no open source
implementation of this that was really
usable so
I didn't really want to buy a software
license for something like this which
would have cost I don't know a few
thousand Euros um I didn't know people
at the time who had the license so I
just didn't do
this um which is kind of again the topic
of the talk how do you do this without
the proper tools um and even worse the
simulation is not even going to tell you
what the actual result is from making
your printed circuit board at at these
frequencies uh you start getting
problems with having Corners in your
traces
where things are just getting reflected
um making your trace on the PCB wider or
smaller can cause Reflections can cause
loss um having wires going through the
board starts becoming a problem so at
some point when you go high enough in
the frequencies and the data rates that
you want to handle you really need to
build the boards measure them take the
feedback into account build them
again as with before I didn't do this
the lab gear for this is Ser ly
expensive um even renting it is very
expensive um I could have shipped it out
to some uh people to measure it um I did
in fact ask for that um and people said
yeah I will measure it for you I
unfortunately Didn't Do It um so the end
result is what I call designed by angst
um so all I could do was basically read
as much as I could find um read the
application notes for the chips I'm
using um try to be as careful as
possible um and use the tools that I
have available um so if I go back to
this
actual uh these uh what's the English
word cuts through the pcbs um those are
for the actual PCB that I ended up
building um and they seem to be not too
far off um and um this is a fun enough
this is a very buried tool from a PCB
Suite that has been discontinued it says
at the bottom it's called alter PCB
tline Sim if uh anyone wants to play
around with that uh you can still find
The Code by digging around on GitHub you
need to build it yourself it's a very
odd tool but this was the the limit of
tools I had access to at the time
um this is basically what ended up being
my my result from just trying to uh I
guess [ __ ] my way through the
design um
so you can see the on the top there's
the four ports for the transceivers that
I mentioned
before I've drawn in uh what what I
could remember in uh in uh in well
precautions to take um some of are kind
of self-explanatory um I did try to
length match the differential pairs
that's the the circle thing on the
bottom left um some application notes
nowadays say that you shouldn't do this
which I didn't understand so I just kept
doing it um I did keep distance between
the different pairs which is something
every data sheet tells you to do um
there's something called the three W
rule or even the five W rule which says
that whatever the distance between your
parses you should have three times or
five times that diff distance as free
area to your other
traces um I did make this design by uh
by keeping everything as short as I
could which then people also told me
that that might not be a good idea
because if you have a short uh line um
it's basically less uh less attenuation
for any Reflections that you may may
have so if your signal signal starts
going back and forth which it can very
much do in at these frequencies if it's
a longer trace it will get attenuated on
the way back and then attenuated again
so your your Reflections die down and
this is this doesn't happen as much if
you have a shorter
Trace
I went with
this um I also used anti pads which is
just punching a hole in the ground plane
that is under the connector in this case
um because the connector has much larger
uh a much larger area on the printed
circuit board where the connector needs
to be soldered onto um and that doesn't
match the behavior of the other traces
on your board so what you do is you cut
a hole in the ground plane and that kind
of compensates for that
um there's some things you can't see in
the diagram U you always have to have a
continuous ground with all of these
things and that ground plane needs to be
directly below your highs speeded traces
or if the highs speed traces are inside
of the board it you need to sandwich it
in uh in power supply planes um you need
to have decoupling for the chips you use
um using Yas makes things really hard so
you can see I was able to get away
without using any wires which probably
if I had to use wires to go to some
other like to the other side of the
board then I'm guessing that this
probably would not have worked um so
yeah the layout in this case worked out
to be fair most chips in this area for
for highspeed signals are designed to
make the layout as easy as possible um I
did also Inver the polarity on some of
the traces here um reversing uh plus and
minus basically inside of the
differential pair uh the chips have a
bit in the output that you can set that
just reverses that and you just need to
set the bit correctly to change it back
um
so the whole point of this talk is did
this work if you know HF then you can
understand it's a yes if you don't know
HF I will explain
shortly what these pictures mean however
if you understand HF you also mean that
it didn't quite work so I can hear a few
laughs um all of these are eye diagrams
um what an eye diagram is is from your
high-speed signal in this case 10 GB
ethernet you take one clock period and
just keep stacking it on top of itself
so looking at these
diagrams you have the signal going from
a one to a one to a one from a one to a
one to a zero or something or from a
zero to a one to a zero that creates
these curves basically and the
horizontal is one period of the signal
um and you just stack it and stack
it and five of these look good the sixth
one in the bottom is actually still okay
but much worse than the other
ones um the good thing in this case is
um that the chip I'm using um has a
built-in monitor for generating these
things because otherwise I would need
the expensive test equipment again to
even get this this debugging information
so that's also
something to point out as as part of
this if you try to build highspeed
Electronics like this absolutely pay
attention to the debugging tools the
chips give you
um something I saw in more expensive
other chips was that they have a
built-in error rate tester which this
one doesn't so I wasn't yet able to run
a bit error rate test um I'm trying to
find ways to to do that um but yeah
having this this eye diagram monitor
it's
Lifesaver now for that middle bottom
diagram um that that's where you really
hit the limitations of building
something like this without the proper
tools I essentially I have no way to
figure out why that one connection is
worse than the others it's probably
still workable but I I'm not comfortable
with seeing that and knowing that five
of my connections are okay and the sixth
one is somehow weird um I was lucky in
this case well lucky is maybe the wrong
word um I did just forgot the forget the
AC coupling capacitors on that
connection um the HF guys may laugh at
me for this um for everyone else I may
need to explain what an AC coupling how
many people don't know what AC coupling
is okay that's enough um so for for a
signal like this um let's go back to
maybe the this um those those two wires
each are one signal and one wire goes in
the positive direction the other goes to
the negative Direction and they go
around a Center Point basically and that
is a DC component that just stays
constant however your receiver may have
a requirement for some specific midpoint
voltage which means that you need to put
a capacitor in the middle so your
receiver can shift the signal somewhere
where it likes it likes to receive it
and these chips have that requirement
and the optical transceivers have this
built in except I have some connections
between the chips where I completely
forgot this so I'm hoping that I can get
away without debugging and um just fix
this for the for the record I noticed
this yesterday um so oops um it does
actually work though which is kind of
funny
um it hopefully is also the reason that
this stuff is getting hot as [ __ ] uh
because if you have some difference in
the DC levels between the two chips the
sender might be outputting like 1.6 volt
common mode and the receiver might might
be trying to pull down to 1.2 volt
common mode and you have just 0.4 volts
being lost somewhere in the middle and
that would explain why the ships are
getting so hot I don't really have the
stuff with me here to try try and fix
this here here so I'll have to go back
um and try and debug this um the other
takeaway here is at some point you need
to ask for help um I did ask both RF guy
and Andrew zberg for help and they both
RF guy already was very helpful gave me
a lot of feedback um Andrew I asked for
actually help in simulating this uh I
got this lost on my end I never sent him
design um
but the point of this talk I guess um is
it is in fact possible to build things
like
this um you need to be extremely careful
about the tools you use in this case the
chip has a lot of built-in debugging
features um so yeah um I kind of
sprinted through my presentation this is
uh I expected this to take 30 minutes it
took 20 at
best um so I
think there's a lot of room for
questions um I also have additional
stories about building this from parts
that are not directly HF stuff um I had
those in the presentation and I lost it
on a broken laptop I'm very sorry about
that do backups I have backups they are
three months
old
oops okay um let's all right so try
maybe to get started does anyone have
basic questions where I should just
explain some more yeah just quickly
before we get to the questions maybe a
big round of applause for
equinox
yeah and if you have questions the mic
row or there will be a queue there for
questions so go to Mike over there with
the mic yeah so thank you for talk uh
great talk I've done a bit of H Chef in
the past I would expect that uh going uh
to 25 gbits would be orders of magnitude
uh harder do you think it would be
possible to do it by hand like you
mostly did um so okay
for uh for context um going to 25
gigabot is not like there's some exp EXP
IAL scaling involved which just makes
things extremely harder uh and I don't
have the knowledge to answer your
question um I am so people have asked me
if it's possible to build something like
this for 25 GB especially because four *
25 is 100 GB link um there are some
chips around that I would like to use
for this the reason I haven't done it
yet is and this is actually an important
thing of this talk that I wanted to do I
want to give a kind of a negative shout
out to one of the vendors in this case
maom um they have the perfect chip for
this but they don't give you access to
the data sheet you can find it like by
Googling but it's only a basic sheet the
chip is perfect for building something
like something like this but they are
extremely dismissive if you try to
contact them and try to get more
information I may have another talk in
two years 3 years about what the story
was with 25 Gig if it worked out um I
would so since at this point key cut is
getting support for I'm losing the
microphone sorry so since Kat is getting
the support for simulating the boards I
would hope that this
is sufficient to stretch the the
possible some more
basically sorry
um I honestly don't know I am I'm the
person who's uh telling how far I was
able to get without knowing how it works
um we we may need to find there were
some people who raised their hands about
being HF Engineers if someone else wants
to uh throw in their two cents I I'm
happy to hear uh
so and the next question uh great talk
and and and you're a hero for attending
this um er you had this really cool
thing about um the monitor of the chip
being used to give you the eye um
diagram uh did you try to maybe do your
own test equipment so that you know to
hack the Chip And just measure other
devices eye diagrams um
so okay um the the chip has built an eye
monitor however the chip only works for
certain ranges of of of signal it's a
lot that it works for so the chip has a
range of either 8 to 10 something or 9
to 12 something gigabot and it can
divide that by 1 2 4 or eight so it
works in kind of some area as you could
connect that to get a rudimentary eye
monitor um I haven't thought about
making my own test tool um I
was hoping that maybe someone would
would build an open source VNA which is
the right tool for this um it might also
be possible to use um uh if you know the
Nano VNA um that's single-ended but if
you combine it with a balloon it might
be possible to do differential
measurements
again so I don't feel comfortable
building a test tool myself with the
limited understanding I have I feel like
I can build an application but I can't
build an actual measurement device
because if you build a measurement
device you should know what you're doing
you know that's
my uh uh yeah sure so for a proper test
equipment yeah sure but just for hacking
around um if you just have some sort of
breakout board to do this I I wasn't
even aware that these chips can do that
so this is really cool you can take a
copper direct attach cable and just cut
it open um that should work if you have
the right signal levels however the
signal levels are mostly the same anyway
for all of this High speeded stuff so
that shouldn't be a problem I would hope
um yeah and then we have the next man so
you said your motivation was like the
cables and the CCH but the CCH tear down
and now rebuild I mean do you see any
other cool stuff you can do I me they
still have the same shitty
fibers
unfortunately oh cool um so if we go
back to Hamburg um I'm not I'm not sure
they have the exact same type I do know
that they still have multimode fiber and
oh I did mention that I wanted to go
into a little bit more detail why
multimo fiber is a problem so normally
when you when the signal gets weaker um
you on the optical signal this is the
electrical signal to be clear on the
optical signal you just get a closer and
closer eye and at some point the
receiver doesn't work anymore with the
shitty multim mode fiber you get
horizontal eye closure because the
signals take different paths and they
get mushier and mushier on the time
domain so the horizontal is the time on
this um I'm not sure if the CCH still
has multimode fiber that is as bad as it
was before I only know that they put
back multimode fiber in general I would
hope that they did maybe replace it um
but yeah so if we go back to Hamburg
which seems likely um we may want to use
those again I don't know
maybe um apart from that um it is
intended as a general fiber tool um it
does have uh batteries it's pocket sized
uh you can just put um transceivers into
it and use it as a helper while you roll
out your network uh we did have multiple
occurrences at buildup during camp where
this would have been useful
unfortunately this is not quite ready
the hardware works I've connected my
laptop to the internet through this at
10 gig so I know it works except the
software still needs to be done so um I
can right now I need to like do I Square
C register rides to set it up correctly
and it wasn't quite ready because I ran
out of time in in in the run up to the
camp so yeah I think it's useful as a
tool sorry next question yeah hi thanks
for your talk and your nice project uh
following up on the 25 gig you are lucky
you you go to Optical transceivers to
converters you traces are all short it's
completely different when you do a
layout that actually goes down to 100 M
copper so this this helps in your case
and you did your proper job in analyzing
and being very careful reading all the
stuff you do the same for 25 gig
probably you have to switch away from F4
space material to get more half RF ready
but it's it's doable you can still do it
with with Kad and analyze with with uh
other FM tools which are open source
around it's just more work and you need
to select properly your PCB window and
allo impedance control which just cost
more money
possibly this is uh going to the more
debug features as you said your chip has
a built-in uh IM monitor but for very
limited frequencies and you don't have
the BET test uh if you interested in
doing debugging with this kind of
features go for fpga development ports
which have SFP modules and you then you
don't have open source TOS then you just
install open uh the tool chain from the
Rend on there you have I I belt or smart
belt yeah features inside the
transceivers of the
fpgs by a development kit with with a
proper layout and done and connect it to
here and then you can still do loop back
tests and get all your features done I
think this is a a really long question
but the finally the question okay yeah
um there are some
fpjsangprobinsyano from from the debug
software like yeah okay I don't know
like I know these features exist um so
if if other people want to know more
about this I guess they can come to you
um and yeah the the vendors certainly
know how to make their boards for the
dev kits because they want to sell their
Hardware uh next question maybe just one
very short question did you try about
talking about the VNA stuff did you try
there's an uh VNA front and IC from
analog ADL 5960 I'm I have become aware
it exists I haven't looked at any of the
details yet
um I it's the same comment as before um
I'm not sure I have enough knowledge to
to look at measuring equipment because
that that Analog Devices ship is really
targeted at building a VNA um and I I
feel like I don't have enough knowledge
to do that I would hope that in general
someone will build an open source to
like that maybe the nanovna people we
just make a I think version six is next
one um but that would very be very cool
um oh I did forget a comment to the
previous um this is also manufactured by
GLC PCB which is cheap Chinese
pcbs so that's another comment on on
like the feasibility of this with 10 gig
you can get away with using
cheap mostly specified pcbs uh the funny
thing is that jlcpcb changed their
specification of their lay stackups
Midway through me building this which is
not nice either um but this is certainly
not Precision pcbs this is just a cheap
four layer board um which also four
layer boards are just cheap enough these
days don't even try to do this with a
two layer board it's not going to work
I'm pretty sure next question yeah I
think yeah just that this is probably
the last question and then if people
want to find you after this to talk to
you where can they find you uh you can
find me in the no I do have 10 more
minutes right yeah
yeah I think we can just fill with
questions right I mean there seems to be
one in CU so yeah I just have a short
comment about something you just said uh
you said that the fbga vendors know how
to build their death boards because they
want to sell them don't count on it it's
okay um
okay uh sure well switch venders don't
know how to build switches either I can
tell you from
experience
um yeah yeah um considering that I have
10 minutes left I can just go into
random other stuff um because oh sorry
there's one more yeah so you asked for
comments from other people who had
experience doing this sort of thing uh I
did a HDMI Matrix switch
ah and then a display port Matrix switch
and uh had very similar experiences to
yours except mostly things just work
yeah it's and I think it's to do with
receiver quality yeah um did you did you
have some some measurement that you
could do to get like some eye diagram or
just some measure of whether you were
barely working or working well uh so I I
did actually do oscilloscope
measurements at low frequencies which
told me something and then I sent the
board to Andrew which told me a lot more
um there is actually an HDMI retim chip
which can which can do I measure um ey
diagrams okay but it's out of stock yeah
well once it's back in stock I'm I'm
also planning to to make a measurement
tool like this yeah this this thing got
delayed by 2 years as well because not
like the microcontroller was just not
available and other chips were just not
available and yeah luckily that
has mostly come to an end um yeah if
people are still interested there's
there's actually two boards in this and
as it turns out U most of the problems
in building this actually came from the
power supply and building a over
complicated environment around all of
the HF stuff um I tried to build this as
power savy as possible
which caused more problems it has
battery charging which has caused
problems so I think the closing sentence
here is
um maybe try one thing first um the HF
stuff can definitely be done um and
don't forget the other stuff um if if I
had been a bit more careful I think I
could have saved myself quite a few
revisions I think this is revision five
or six of this board as far as
manufacturing goes I do have prototypes
with me if people want to go look at the
actual PCB um you can find me in the
knock uh which is over there near the uh
fence to the camping area it's a white
tent uh please be uh polite SL
restrained when entering the tent it's
possible that people are working to
debug the network so if there's like a
rush of activity then maybe come back a
little bit
later um I haven't actually pushed this
out on GitHub yet I plan to do that um
you can find me on masteron
uh Equinox at chosocial
um my GitHub is linked from masteron and
I think
that's yeah cool thanks for attending
big round of
[Applause]
applause