[SI-LIST] Re: Eye Diagram Question

Hi Jeff

If you only had band-limiting(low-pass elements) the eye would be 
symmetrical except for:

    Group Delay =differential phase distortion,  similar to a 
charge/discharge integrated waveform,

However, with reflections along the line, these reflections can add or 
subtract at anywhere
within the eye.  I have found that adjustment of the line lengths 
(relative to a constant data rate)
can shift secondary reflections to any location in the eye.  If the data 
time interval matches the delay
time of the channel (actually half) or any integer multiple, the zero 
transitions coincide so PLL
clock regeneration is most accurate and the eye usually looks the best.

BTW, I assigned a patent application to Brocade for this trick.

Ron Miller




 Hi,

>>What would cause an eye digaram to be asymmetric between the left and
>>right hand sides?  I am looking at an eye that has a left hand side that
>>has a very shallow rise/fall to the respective zero and one levels. The
>>right hand side has much sharper rise/fall.  I understand there are
>>frequency dependent losses, but I would *think* that would affect both
>>sides of the eye in the same way.  I played with preemphasis in the
>>driver - but didn't see much effect.
>>
>>Any ideas what this might be / not be?  ISI, reflection, etc?
>>
>>Thanks,
>>Jeff
>>
>>
>>    
>>

-- 
Ronald B. Miller, Microwave/SI Engineer  RAIL = NOISE + REFLECTIONS
Gigahertz Data Div of MI Corp.              \\  //         \\  // 
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Newark,  CA  94560                      ->JITTER<-   EYE   ->JITTER<-
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