[T10] Questions about SAS coefficients' configuration

Harvey Newman harvey.newman at avagotech.com
Fri Nov 20 06:42:56 PST 2015


Hi Jia,

There is one key point that needs to be reviewed.  That is the location of
the compliance point ITs is found on the side of the connector nearest to
the Tx. This can be seen in Figure 12.

Note the title of Table 47 lists the compliance point as ITs or CTs.

The Tx return loss does not include the reflection from the connector.

Please let me know if the resolves your concern.
[image: Inline image 1]
Regards,
Harvey Newman
Avago Technologies

On Fri, Nov 20, 2015 at 2:06 AM, Jiagongxian <jiagongxian at huawei.com> wrote:

> HI All,  I have a question related  to  SAS TX  RX  common mode return
> loss, according to the SAS 3r06,     for 12Gbps TX, the common mode loss
> requirement is as the following,
>
>
>
>
>
> Which is measured as the following method,
>
>
>
> The  return loss of  device is defined at the connector pin according the
> document.
>
>
>
>
>
> Which means,  after de-embeddng,  TX or RX return loss is mainly
> influenced by the connector, if the return loss of  SAS  connector is
> high,  it will make the return loss of the device can not meet the spec. of
> TX or RX side of SAS device.
>
>
>
> Unfortunely, the  SAS connector requirement is as the following,
>
>
>
>
>
> Compare Table 47 (return loss requirement of  SAS device) and Table 7
> (return loss of  SAS connector ) ,  the common mode return loss of
> connector is about -3 dB, while that of  device is beginning with -6 dB,
> which make it is very hard for  the  device’s common mode return loss  to
> pass -6 dB spec.  at lower frequency band.
>
>
>
> Is there anything wrong  with my analysis ?
>
>
>
> Best regards
>
>
>
> Jia Gongxian/贾功贤
>
> Phone: 0755-89651131
> Email: jgxian at huawei.com
> Huawei Technologies Co., Ltd./华为技术有限公司
> Bantian, Longgang District,Shenzhen 518129, P.R.China/深圳市龙岗区坂田华为基地,518129
> http://www.huawei.com
>
>
> -------------------------------------------------------------------------------------------------------------------------------------
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>
> *发件人:* owner-t10 at t10.org [mailto:owner-t10 at t10.org] *代表 *Yupengfei (B)
> *发送时间:* 2015年3月24日 19:04
> *收件人:* t10 at t10.org; Harvey Newman
> *抄送:* Ningzuolin; Guojian (F); Yangjunbin (Jim, HS); Chenlili (E)
> *主题:* Re: Questions about SAS coefficients' configuration
>
>
>
> Hi Harvey,
>
>
>
> Here are our understandings about the figure “Minimum and maximum
> coefficient ranges at maximum peak to peak voltage”:
>
>
>
> (1)   |C1|+C2+|C3|<=1, thus *C2<=1-|C1|-|C3|*, and “C2 at maximum”
> represents *C2=1-|C1|-|C3|* in the figure, which means Vp-p is always
> constrained by C2=1-|C1|-|C3|.
>
> This is how I understand your words “Keep in mind that this figure is
> defined with C2 at maximum.”. Right?
>
>
>
> (2)   The specifications of “Table 43 – Transmitter device signal output
> characteristics for trained 12Gb/s at ET, IT, and CT” imply *0>=C1>=-0.2*
> and *0>=C3>=-0.35*. Besides, *C2-|C1|-|C3|>=X*, (X=VMAmin/2K0, refer
> Table 48).
>
> The purple line is drawn according to the above 3 constraints, and dash or
> solid just represents the legal possible real differential peak to peak
> output voltage “at maximum peak to peak voltage”.
>
> The red line represents the points with possible minimum non transition
> bit differential output voltage (i.e. VMA) “at maximum peak to peak
> voltage”, especially *Point x* located at the left bottom corner.
>
> So, we can see,
>
> (a)   The * Point x* generates the minimum VMA within the red line, so *VMAx>80mV
> should be satisfied*.
>
> (b)   *If 850mV<=Vpp_noeq<=1200mV is meet, VMAx>80mV is satisfied too.*
> Because Vpp_noeq*(C2-|C1|-|C3|)>=850mV*(0.55-0.15-0.3)=85mV>80mV.
>
> Finally, 2 conclusions can be made from the figure in my opinion.
>
> (A)   *A Transmitter should guarantee the coefficient ranges located on
> red dash line*, so that Rpre=1.66 and Rpost=3.33 in Table 43 will be
> obtained.
>
> (B)   *A Transmitter should guarantee 850mV<=Vpp_noeq<=1200mV*, so that
> VMA>80mV in Table 43 will be obtained when (A) is satisfied.
>
> Of course, both (A) and (B) are “at maximum peak to peak voltage”.
>
>
>
> (3)   We agree with your answer “Since my answer to 2a was no we need to
> address question 2b that starts ‘If yes,’. We wanted to provide the
> receiver the ability to adjust C2 and lower the amplitude. We have placed
> the responsibility of maintaining the VMA >= 80 mV on the transmitter. We
> believe this provides the required constraints.”, but I think *“maintaining
> VMA>=80mV” is implemented by constraining C2-|C1|-|C3| which is equivalent
> to VMA/2K0* just like 1 is equivalent to Vpp_noeq.
>
>
>
> (4)   The specification *850mV<=Vpp_noeq<=1200mV* is defined only when
> “C2 at maximum”. So, when C2 is reduced, the differential peak to peak
> output voltage does not need to satisfy *850mV<=Vpp_noeq<=1200mV*, right?
>
>
>
> (5)   I think a SAS3.0 compliant Transmitter shall meet the following
> constraints according to (1)-(4), right?
>
> *a)        **|C1|+C2+|C3|<=1*
>
> *b)       **|C1|<=0.2*
>
> *c)        **|C3|<=0.35*
>
> *d)       **C2-|C1|-|C3|>=X, X=VMAmin/2K0.*
>
>
>
> (6)   “Table 48 – 12Gb/s reference transmitter device characteristics at
> ET” gives a different coefficient range C1>=-0.15 and C3>=-0.3, which does
> not match with Table 43. Why?
>
>
>
> We are expecting your comments about our understandings above.
>
> Thank you!
>
> Pengfei Yu
>
>
>
>
>
> //-------------------------
>
>
>
>
>
> Hi Pengfei,
>
>
>
> The figure you are asking about was the subject of a lot of discussion
> during the specification development. It has been the subject of additional
> discussion following the release of this document as well. Let me try and
> provide some insights that hopefully provides you and everyone else a
> consistent interpretation.
>
>
>
> I start with the title of the figure "Minimum and maximum coefficient
> ranges at maximum peak to peak voltage". When writing the specification we
> realized the range the coefficients are capable of adjusting to on the
> transmitter impacted the amount of equalization available to the over all
> budget. In order to assure compatibility we needed to have some way to
> require all SAS-3 compliant transmitters to support a minimum specified
> range of the coefficients. Due to the interdependence between coefficient
> range and amplitude we attempted to specify the range of the coefficients
> when the amplitude (C2) was at maximum.
>
>
>
> Maximum amplitude is limited by the 1200 mV differential peak to peak
> number covered elsewhere in the specification. This limit is written into
> the specification to protect receivers both now and in the future from
> being over driven. Because it is a shall not exceed number all transmitters
> are required to stay below this value when the coefficient C2 responds with
> Maximum to an Increment command. The allowed voltage range for a
> transmitter with C2 at maximum is 1200 mV to 850 mV. See SPL3r07 section
> 5.14 for details on the phy layer transmitter training coefficient
> adjustments.
>
>
>
> With C2 at maximum "...at maximum peak to peak voltage" the figure places
> limits on the C1 and C3 "Minimum and maximum coefficient ranges". There was
> concern that as amplitudes reduce we did not want the non-transition bit
> (i.e., VMA) amplitude to fall below 80 mV differential peak to peak. The
> dashed purple line is intended to communicate that the coefficient range
> might be limited by the VMA requirement for lower amplitude signals. Keep
> in mind that this figure is defined with C2 at maximum. Therefore we do not
> need to add a constraint “C2-|C1|-|C3|>=Fixed Value” because C2 is not a
> variable for the purpose of these limit lines.
>
>
>
> Now to your questions.
>
> Question 1:
>
> Whether the value of C1 and C3 is the total value surrounding by the
> purple solid line when Vpp_noeq = 1200mv?
>
> Answer 1a:
>
> The purple solid line represents the maximum range of C1 and C3 when C2 is
> at maximum.
>
> Question 1b:
>
> If so, does it mean the value of C1 and C3 in purple solid line satisfied
> equation “VMA>=80mv” when Vpp_noeq=1200mv?
>
> Answer 1b:
>
> If the amplitude of the signal is very close to the 1200 mV amplitude then
> the VMA limit should be reached along the lower left diagonal limit line.
> If the amplitude of the signal is lower, then the VMA limit will be the
> limiting factor causing the maximum range to move in the direction
> indicated by the dashed purple line.
>
>
>
> Question 2:
>
> Do we need a constraint like “C2-|C1|-|C3|>=Fixed Value” to ensure “
> VMA>=80mv” when Vpp_noeq is variable between 850mv and 1200mv?
>
> Answer 2a:
>
> Since the figure applies when C2 is maximum we do not need to add the
> constraint because for the purpose of this figure C2 is not a variable. As
> soon as C2 is adjusted this figure does not apply. The VMA >= 80 mV always
> applies and provides the primary maximum bound for C1 and C3 once C2 has
> been reduced.
>
> Question 2b:
>
> If yes, when we constraint “C3>=-0.3” and “C1>=-0.15”(the range
> surrounding by the red dotted line shown in Figure 131, which is the
> minimum range we should support), we do not need the constraint “C2-|C1|-|C3|>=Fixed
> Value” or any other constraint of C2 to ensure the minimum value of VMA,
> right?
>
> Answer 2b:
>
> Since my answer to 2a was no we need to address question 2b that starts
> "If yes,". We wanted to provide the receiver the ability to adjust C2 and
> lower the amplitude. We have placed the responsibility of maintaining the
> VMA >= 80 mV on the transmitter. We believe this provides the required
> constraints.
>
>
>
> Please let me know if there are additional questions.
>
>
>
> Regards,
>
> Harvey Newman
>
> Avago Technologies
>
>
>
> On Mon, Mar 16, 2015 at 7:50 PM, Yupengfei (B) <yu.yupengfei at hisilicon.com>
> wrote:
>
> Hi All,
>
>
>
> I have questions needing your help.
>
>
>
> In SAS-3R06’s Figure 131 -- “Minimum and maximum coefficient ranges at
> maximum peak to peak voltage”,
>
> it defines the minimum range and maximum range of C1 and C3 with different
> Vpp_noeq.
>
>
>
> Question 1:
>
> Whether the value of C1 and C3 is the total value surrounding by the
> purple solid line when Vpp_noeq = 1200mv?
>
> If so, does it mean the value of C1 and C3 in purple solid line satisfied
> equation “VMA>=80mv” when Vpp_noeq=1200mv?
>
>
>
> Question 2:
>
> Do we need a constraint like “C2-|C1|-|C3|>=Fixed Value” to ensure “
> VMA>=80mv” when Vpp_noeq is variable between 850mv and 1200mv?
>
> If yes, when we constraint “C3>=-0.3” and “C1>=-0.15”(the range
> surrounding by the red dotted line shown in Figure 131, which is the
> minimum range we should support), we do not need the constraint “C2-|C1|-|C3|>=Fixed
> Value” or any other constraint of C2 to ensure the minimum value of VMA,
> right?
>
>
>
> Best Regards,
>
> Pengfei Yu
>
>
>
>
> ------------------------------
>
>
> 华为技术有限公司 Huawei Technologies Co., Ltd.
> [image: Company_logo]
>
> Phone:
> Fax:
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> Huawei Technologies Co., Ltd.
> Bantian, Longgang District,Shenzhen 518129, P.R.China
> http://www.huawei.com
> ------------------------------
>
> 本邮件及其附件含有华为公司的保密信息,仅限于发送给上面地址中列出的个人或群组。禁
> 止任何其他人以任何形式使用(包括但不限于全部或部分地泄露、复制、或散发)本邮件中
> 的信息。如果您错收了本邮件,请您立即电话或邮件通知发件人并删除本邮件!
> This e-mail and its attachments contain confidential information from
> HUAWEI, which
> is intended only for the person or entity whose address is listed above.
> Any use of the
> information contained herein in any way (including, but not limited to,
> total or partial
> disclosure, reproduction, or dissemination) by persons other than the
> intended
> recipient(s) is prohibited. If you receive this e-mail in error, please
> notify the sender by
> phone or email immediately and delete it!
>
>
>
>
>
>
>
> --
>
> Harvey Newman
>
> Avago Technologies
>
> (408) 433-4028
>
> _______________________________________________
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>


-- 
Harvey Newman
Avago Technologies
(408) 433-4028
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