[SI-LIST] Re: Minimum eye opening of 8b10b encoded signals
- From: "T.K. Jeon" <tkjeon@xxxxxxxx>
- To: dave.instone@xxxxxxxxxx
- Date: Wed, 23 Mar 2005 14:35:22 -0800
Hi Dave,
Speaking of Tx min vtg measurement interval, although the Table 4 does
not say the interval for Gen1i/m, Clause 6.4.2.1 explains how to measure
the min amplitude and it says the measurement interval is in [0.45UI,
0.55UI]. I guess that there should be a note for clarification saying
whether the clause applies to both Gen1i/m and Gen2i/m or not.
And, SATA II Clause 6.4.4(page 117) states 'The minimum amplitude value
is measured 0.5UI after a reference clock edge' for Tx amplitude not
specifying Gen*i or Gen*m or Gen*x, which may also need some clarification.
Regards,
TK
Dave Instone wrote:
> Hi TK,
> according to the SATA II spec Table 4, for Gen1i and Gen1m there is
> no Tx minimum Voltage measurement interval specified, in fact there are
> many holes in that table for 1i and 1m and my interpretation of 6.1.1
> of SATA II is that it states, somewhat unclearly, that the existing SATA
> 1 spec applies to these variants. SATA 1.0a does show an eye although
> it states ' The EYE is more of a qualitative measurement than a
> spec.........Nonetheless this method is useful and easy to set up in the
> lab.'
>
> Regards
> Dave Instone
> T.K. Jeon wrote:
>
>
>>Hello Michael,
>>
>>I'm not sure if you make measurements on SATA 1.0 or SATA II. But,
>>SATA II specifies 'min/max amplitude', but not the eye opening.
>>Therefore, there is no eye mask specified in the standard. I'm saying
>>SATA II because I guess it's the latest spec.
>>
>>On SATA II, the min amplitude measurement is based on statistical
>>distributions from n samples collected between 0.45UI and 0.55UI using
>>three different patterns, which are HFTP(high frequency pattern),
>>MFTP(middle freq. pattern) and LBP(lone bit pattern).
>>
>>Regards,
>>TK
>>
>>Dave Instone wrote:
>>
>>
>>>Dear Michael,
>>> The question of where to position the eye has been the subject of
>>>many many discussions in Fibre Channel (which also uses 8b10b)and
>>>also I suspect in SATA as a lot of the work of the Fibre Channel
>>>jitter methodology appears in the SATA spec. As yet no single answer
>>>has been decided. Essentially it depends on how the clock recovery
>>>circuit centers itself. The majority view is that you determine the
>>>mean of the crossing and place the mask such that 0 UI is on the
>>>mean, this will be correct for mean following CRCs. However if the
>>>jitter distribution is skewed this can result in a lot of margin in
>>>one direction, and much less in the other, there are also
>>>oversampling type SERDES which may center themselves differently and
>>>there are also SERDES which used undisclosed methods of
>>>'compensating' for skewed distributions. To be safe you should use
>>>the mean of the crossing to position the mask.
>>> Regarding your particular violations you don't say if you are
>>>looking at the Rx end or the Tx end. If at the Rx end it seems to me
>>>that your link has too much HF loss, alternatively the TX risetime
>>>could be too slow and/or its amplitude too low.
>>>Regards
>>>Dave Instone
>>>
>>>Michael.Kurten@xxxxxxxxxxxxxxxxxxx wrote:
>>>
>>>
>>>
>>>>Hello all,
>>>>
>>>>I have a question with regard to the minimum eye opening. I'm examining
>>>>an SATA link which has 8b10b encoding. The measured eye opening does
>>>>not
>>>>exhibit a lot of jitter. Therefore the double trapezoid, describing the
>>>>minimum eye opening, can be shifted along the time axis. The eye height
>>>>instead violates massively the minimum eye opening if the minimum
>>>>eye is
>>>>centered or placed at the left corner of the measured eye. Shifting the
>>>>minimum eye opening to the right corner results in an only slightly
>>>>violated minimum eye opening.=20
>>>>To date my understanding is that if the minimum eye opening can be
>>>>placed anywhere along the time axis and not violating the eye opening
>>>>the link will work fine. Otherwise the minimum eye opening would not be
>>>>the minimum eye opening. But now I am looking for a more hardware
>>>>oriented explanation of this matter.
>>>>Any help is highly appreciated.
>>>>
>>>>Kind regards
>>>>Michael Kurten
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>>>>
>>>
>>>
>>>
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>>
>>
>>
>>
>
>
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