[SI-LIST] Re: Rx Eye Mask width, BER, and Jitter

  • From: "Murphy, Martin" <Martin.Murphy@xxxxxxxxxxx>
  • To: "Conrad Herse" <herse@xxxxxxxxxxxxxxxxxx>
  • Date: Mon, 21 Jun 2010 14:15:28 -0700

Conrad,

The Rx minimum eye width spec is a number that would usually be tied to
a particular BER target spec; eg 0.2UI at 10e-12 BER. As you pointed out
in your example, the resultant maximum allowable TJ of 0.8UI will be
composed of a DJ number and 14*RJ for the Dual Dirac model at the 10e-12
BER level.

For that combination of DJ and RJ, your eye margin at 10e-15 BER will
obviously be smaller, and you can work out the margin using the 1UI -(DJ
+ 15.883*RJ) calculation. Note: this does not imply that jitter
tolerance is increased. The tolerance to jitter hasn't changed at all,
just your reference point for an eye margin measurement.

If you really want 0.2UI of receiver eye margin at 10e-15 BER, then
start with those numbers and you'll obviously calculate backwards to a
wider eye margin at 10e-12.


Martin Murphy
Anritsu
  

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Conrad Herse
Sent: Monday, June 21, 2010 1:49 PM
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Rx Eye Mask width, BER, and Jitter

Hi Jim,

Maybe this is what's confusing me. The receiver specifies a jitter
*tolerance*. From this an Rx minimum eye width can be determined. I
would expect the min required eye width to *grow* when going to
BER=1e15, since the receiver must *tolerate* more jitter. Making the min
Rx eye mask smaller at BER=1e-15 doesn't seem correct, it implies the Rx
jitter tolerance increases at 1e-15. Again, I'm referring to the Rx
jitter tolerance and what the receiver requires, I understand that the
actual eye size at the receiver will decrease when more jitter is
budgeted into the system.

Thanks,

Conrad Herse



James.Mueller@xxxxxxxxxx wrote:
> Hi Conrad,
> 
> When you went to calculate the mask size at BER= 1E-15, you added the
> additional rms jitter contribution instead of subtracting.
> 
> Jim
> 
> 
> 
> James J Mueller
> LeCroy Corporation
> Cell phone:     914-522-8555
> 
> 
> 
>

>   From:       Conrad Herse <herse@xxxxxxxxxxxxxxxxxx>

>

>   To:         si-list@xxxxxxxxxxxxx

>

>   Cc:         herse@xxxxxxxxxxxxxxxxxx

>

>   Date:       06/21/2010 03:41 PM

>

>   Subject:    [SI-LIST] Rx Eye Mask width, BER, and Jitter

>

>   Sent by:    si-list-bounce@xxxxxxxxxxxxx

>

> 
> 
> 
> 
> 
> Hello experts,
> 
> I've been working on trying to scale receiver eye mask widths to
> different bit error rates. There is something which is puzzling me
which
> I'm hoping someone can clear up for me.
> 
> I've been studying the dual-Dirac jitter model given by the formula:
> 
> Tj = Dj + 2Q * Jrms
> 
> where Q is a constant from the Complimentary Error function for a
given
> BER (2Q*Jrms = Rj at a specific BER). So if I have a receiver with the
> following jitter tolerance spec:
> 
> Tj = 0.8 UI
> Dj = 0.3 UI
> Rj = 0.5 UI
> BER = 1e-12
> 
> then, given 2Q = 14 for BER = 1e-12:
> 
> Jrms = 0.5 / 14 = 0.036 UI
> 
> The Rx eye mask width would be:
> 
> 1 - 0.8 = 0.2 UI
> 
> If I want to scale the Rx eye mask width to BER=1e-15 I would expect I
> need to *grow* the eye mask width by Jrms.
> 
> Given that 2Q = 15.883 at BER = 1e-15, then my new eye mask width
would be:
> 
> 0.2 + (15.883 - 14) * 0.036 = 0.268 UI
> 
> So far so good, assuming I did this correctly. Here's what puzzles me,
> if I adjust my Rx jitter tolerance to accommodate the new Rx eye mask:
> 
> Tj = 1.0 - 0.268 = 0.732 UI
> Dj = 0.3 UI
> Rj = 0.732 - 0.3 = 0.432 UI
> BER = 1e-15
> 
> and recalculate Jrms:
> 
> Jrms = 0.432 / 15.883 = 0.027 UI
> 
> The Jrms number has changed, I wouldn't expect this to happen simply
> because I'm extrapolating to a different BER. Can someone please
> straighten me out?
> 
> Thanks!
> 
> --
> Conrad Herse
> 
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