[SI-LIST] understanding acceptable amount of jitter for given receiver/system
- From: eric silist <ericsilist@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 28 Aug 2014 17:23:50 -0400
Hi all,
I'm having trouble trying to understand how to define what an
acceptable amount of jitter would be for my serial link. I imagine this
is very broad question but I'm trying to wrap my head around the basics. I
have an ibis model for my transmitter and receiver and I've hooked them up
in spice along with an s-parameter model of my channel. I was pretty happy
with myself that I got this part to work :)
Then I get some outputs that I'm used to looking at, eye diagram, ber
contour, bathtub. I can play with settings in the model and get more open
or closed eyes. So that was fun.
Then I thought how do I tell, and tell someone else whether this data we
are looking at is good enough to meet our target BER or not? For voltage I
went into the serdes datasheet and saw that it was adjustable but the
threshold voltage for signal detect was say 50mV diff. So then I believe
that as long as over 1E-12 bits, my lowest vertical eye opening is not
lower than 50mV diff then that would be acceptable. I'm sure some margin
would also be nice.
Next I wanted to understand the same thing for jitter. I started by
looking at the bathtub curve at 1E-12 which I think is just telling me, "if
you ran 1E-12 bits, based on probability this is the eye opening you would
see".
My question is how do I relate this data back to the receiver
requirements/spec to decide if it looks good or not? I think I understand
that what can screw the receiver up would be the clock recovery circuit to
lose it's lock. There is one spec in the receiver that says total receive
input jitter can be 1UI-pkpk. That seems really high though since I'd
think that would mean the eye was completely closed.
Anyway I'm a little stuck, I've tried to do some reading and I've found
lots about what a bathtub curve is, what jitter is etc, but nothing so far
that ties it back to the real world for me. I guess in the past it's
always been defined for me by the spec, but now I find myself wanting to
understand more about it.
Thank you,
-Eric
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