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

  • From: James.Mueller@xxxxxxxxxx
  • To: Conrad Herse <herse@xxxxxxxxxxxxxxxxxx>
  • Date: Mon, 21 Jun 2010 16:16:23 -0400

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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