[SI-LIST] Re: 答复: 答复:答复: HDMI Frequency Failing RE Test by 7dB!!!!
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 01 Jun 2012 07:10:16 -0400
Vinod
As someone commented yesterday, you have common mode getting on the
HDMI. moving cables just changes the radiating antenna configuration.
Scott McMorrow
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On 6/1/2012 2:27 AM, vinod ah wrote:
> Hi all,
>
> One more interesting observation which gave another 2 dB margin. We
> have Ethernet connector adjacent to 2 HDMI connectors. When we
> replaced the un-shielded Ethernet cable with shielded Ethernet cable,
> we got additional 2 dB margin. So we have 4.5dB margin!!!!!!!!!!!!!!.
> But i am not able to understand how is Ethernet cable to do with HDMI
> frequencies?? Is the ethernet cable picking up the radiation from
> adjacent HDMI cable and radiating?? Does this indicate the HDMI cable
> is not properly shielded or is having high common mode current?
>
> Regards
> Vinod A H
>
> On Wed, May 30, 2012 at 6:11 PM, DAVID CUTHBERT<telegrapher9@xxxxxxxxx>
> wrote:
>> Your system has common-mode (antenna) current on the cable shields.
>>
>> Dave Cuthbert
>>
>>
>> On Wed, May 30, 2012 at 12:53 AM, vinod ah<ah.vinod@xxxxxxxxx> wrote:
>>> Hi all,
>>>
>>> I Got additional 2.5dB margin which i was looking for, after
>>> re-routing the cables. The 2 HDMI cables were overlapping earlier, but
>>> when i separated them i got the additional margin. So is it possible
>>> to explain why it so happened? Why i am asking is, the cables used are
>>> shielded cables, so overlapping or non-overlapping should not have
>>> mattered right?
>>>
>>> Regards
>>> Vinod A H
>>>
>>> On Mon, May 28, 2012 at 6:20 PM, steve weir<weirsi@xxxxxxxxxx> wrote:
>>>> 1) Metallize the enclosure and bond the cable shield to that.
>>>> 2) Modify the differential pair trace routes and/or add CM magnetics /
>>>> structures to minimize even mode current.
>>>> 3) Make the image plane part of the PCB.
>>>> 4) Further improve the bond between the cable shield and the PCB.
>>>> 5) Optimize the ferrite used over the cable.
>>>> 6) Introduce PCB trace structures that load the signals with a notch at
>>>> 742MHz.
>>>>
>>>> Steve.
>>>> On 5/28/2012 2:43 AM, vinod ah wrote:
>>>>> HI All,
>>>>>
>>>>> I had been to EMC lab for testing and here are the results.
>>>>>
>>>>> 1) With image plane addition to the HDMI shield pins and shield pins
>>>>> grounded directly to ground at multiple points, there was 4 dB
>>>>> reduction in radiation level.
>>>>>
>>>>> 2) With Only shield pins grounded directly to ground at multiple
>>>>> points, there was 2dB reduction in radiation level.
>>>>>
>>>>> 3) With ferrite clamp on the HDMI cables, there was 2dB reduction in
>>>>> radiation level at 742MHz.
>>>>>
>>>>> 4) Reducing the voltage swing of HDMI signals gave another 0.5dB
>>>>> reduction in radiation level
>>>>>
>>>>> 5) By turning on On-Die series termination in the HDMI TX output
>>>>> drivers, we could get another 0.5dB reduction in radiation level.
>>>>>
>>>>> 6) During ambient readings i.e. Blu ray player connected to TV through
>>>>> HDMI cable, the 742MHz is passing by 8dB only. Previous lab visits,
>>>>> the EMC lab person had shown us Min envelope instead of Max envelope
>>>>> during peak scan, thus mis-leading us to think that the setup is not
>>>>> contributing to the radiation.
>>>>>
>>>>> So Although i am just passing the FCC limits, is there anything i can
>>>>> do to make it pass by some margin, so that in final certification i
>>>>> have some confidence of passing FCC ? Is the setup which itself is
>>>>> passing by 8dB is acceptable to use or should i try some other setup?
>>>>> Currently i am using Sony Blu ray player, LG TV and Copper shielded
>>>>> HDMI cable with ferrite clamp. Is there any better Blu ray players or
>>>>> TV is suggested for final certification?
>>>>>
>>>>> Regards
>>>>> Vinod A H
>>>>>
>>>>> On Fri, May 25, 2012 at 8:28 AM, Zhenwei Wang (zhenwwan)
>>>>> <zhenwwan@xxxxxxxxx> wrote:
>>>>>> One suggestion:
>>>>>>
>>>>>> The most possible way to confirm if the return current through
>>>>>> shielding
>>>>>> line cause EMI issue (as mentioned by Vend +7db above FCC limitation)
>>>>>> is
>>>>>> that:
>>>>>>
>>>>>> 1. Open the shielding line of each TMDS signal pair in ONE END,
>>>>>> prefer
>>>>>> in own board.
>>>>>>
>>>>>> 2. Keep HDMI_DDC ground for functional operation.
>>>>>>
>>>>>> 3. Measure the EMI in lab with same environment.
>>>>>>
>>>>>> If no return current through shielding line, the measurement will be
>>>>>> as same
>>>>>> as before.
>>>>>>
>>>>>> If some return current through HDMI_DDC ground, EMI will be much
>>>>>> bigger than
>>>>>> 7db above FCC limitation.
>>>>>>
>>>>>>
>>>>>>
>>>>>> BR
>>>>>>
>>>>>> Zhenwei(Jason) Wang
>>>>>>
>>>>>> Cisco Systems (Shanghai) Video Technology Co., Ltd.
>>>>>>
>>>>>>
>>>>>>
>>>>>> 发件人: Traa, Boris [mailto:boris.traa@xxxxxxxxxxx]
>>>>>> 发送时间: 2012年5月24日 18:22
>>>>>> 收件人: Zhenwei Wang (zhenwwan); Long Yang
>>>>>> 抄送: ah.vinod@xxxxxxxxx; SI-LIST
>>>>>> 主题: RE: [SI-LIST] 答复: 答复: HDMI Frequency Failing RE Test by 7dB!!!!
>>>>>>
>>>>>>
>>>>>>
>>>>>> Dear Zhenwei Wang,
>>>>>>
>>>>>>
>>>>>>
>>>>>> By calculations it can be concluded that intra-pair skew of a
>>>>>> differential
>>>>>> pseudo random bit stream will only result in a low level wide band EMI
>>>>>> without spectral lines.
>>>>>>
>>>>>>
>>>>>>
>>>>>> In case of non equal rise and fall times this will lead to spectral
>>>>>> lines
>>>>>> that are 6 dB lower for PRBS compared to clock.
>>>>>>
>>>>>>
>>>>>>
>>>>>> Kind regards
>>>>>>
>>>>>> Boris Traa
>>>>>>
>>>>>> System design engineer EMC
>>>>>>
>>>>>>
>>>>>>
>>>>>> It's the currents that make circuits work or fail.
>>>>>>
>>>>>>
>>>>>>
>>>>>> Philips Innovation Services/EMC center
>>>>>>
>>>>>> Room 2.020
>>>>>>
>>>>>> High Tech Campus 26
>>>>>>
>>>>>> 5656AE Eindhoven, The Netherlands
>>>>>>
>>>>>> Tel: ++ 31 40 27 43766
>>>>>>
>>>>>> Fax: ++ 31 40 27 42224
>>>>>>
>>>>>> E-mail: boris.traa@xxxxxxxxxxx
>>>>>>
>>>>>>
>>>>>>
>>>>>> From: Zhenwei Wang (zhenwwan) [mailto:zhenwwan@xxxxxxxxx]
>>>>>> Sent: Thursday 24 May 2012 11:49 AM
>>>>>> To: Long Yang
>>>>>> Cc: Traa, Boris; ah.vinod@xxxxxxxxx; SI-LIST
>>>>>> Subject: 答复: [SI-LIST] 答复: 答复: HDMI Frequency Failing RE Test by
>>>>>> 7dB!!!!
>>>>>>
>>>>>>
>>>>>>
>>>>>> If the intra-pair skew is too much bigger, the cross-point of Data+
>>>>>> and
>>>>>> Data- will not stand on the virtual ground. Then DC return current
>>>>>> will flow
>>>>>> through a ground line. You know every line has inductance. So the
>>>>>> noise can
>>>>>> be get with equation V=Lx(did/dot). The power of return current could
>>>>>> be
>>>>>> radiate through long cable.
>>>>>>
>>>>>> Maybe the reason I said was not the dominant part. We needs
>>>>>> information to deny it.
>>>>>>
>>>>>>
>>>>>>
>>>>>> BR
>>>>>>
>>>>>> Zhenwei(Jason) Wang
>>>>>>
>>>>>> Cisco Systems (Shanghai) Video Technology Co., Ltd.
>>>>>>
>>>>>>
>>>>>>
>>>>>> 发件人: Long Yang [mailto:long.0.yang@xxxxxxxxx]
>>>>>> 发送时间: 2012年5月24日 17:38
>>>>>> 收件人: Zhenwei Wang (zhenwwan)
>>>>>> 抄送: Traa, Boris; ah.vinod@xxxxxxxxx; SI-LIST
>>>>>> 主题: Re: [SI-LIST] 答复: 答复: HDMI Frequency Failing RE Test by 7dB!!!!
>>>>>>
>>>>>>
>>>>>>
>>>>>> Skew should be related to stand-wave antenna resonance.
>>>>>>
>>>>>> On Thu, May 24, 2012 at 2:11 AM, Zhenwei Wang (zhenwwan)
>>>>>> <zhenwwan@xxxxxxxxx> wrote:
>>>>>>
>>>>>> Hi Boris,
>>>>>> Actually, I am just guessing. EMI issue has three key features:
>>>>>> Aggressor, Coupling trace and Receiver. Based Vine's description, the
>>>>>> HDMI
>>>>>> cable acted as the coupling trace in his design. But when the same
>>>>>> cable
>>>>>> connected Sony Blue ray disc and TV, the radiation disappear(Vend did
>>>>>> not
>>>>>> say that directly). So I guessed that in one or two or three TMDS
>>>>>> differential pair, some shielding line worked as the antenna to
>>>>>> radiate the
>>>>>> bit clock frequency.
>>>>>> BTW, if have a HDMI SI report(especially intra-pair skew or
>>>>>> cross-point of TMDS), the guessing will be clear. I know the feeling
>>>>>> when
>>>>>> EMC test failed, much more pressure. So good luck to Vend.
>>>>>>
>>>>>> BR
>>>>>> Zhenwei(Jason) Wang
>>>>>> Cisco Systems (Shanghai) Video Technology Co., Ltd.
>>>>>>
>>>>>>
>>>>>> -----邮件原件-----
>>>>>>
>>>>>> 发件人: Traa, Boris [mailto:boris.traa@xxxxxxxxxxx]
>>>>>> 发送时间: 2012年5月24日 16:34
>>>>>> 收件人: Zhenwei Wang (zhenwwan); ah.vinod@xxxxxxxxx; SI-LIST
>>>>>> 主题: RE: [SI-LIST] 答复: HDMI Frequency Failing RE Test by 7dB!!!!
>>>>>>
>>>>>>
>>>>>> Dear Zhenwei Wang,
>>>>>>
>>>>>> Assuming the data is pseudo random, do you think that inter and intra
>>>>>> pair
>>>>>> skew will cause clock related spectral lines. I'm would think that EMI
>>>>>> will
>>>>>> look like wide band noise. Only in case of different rise and fall
>>>>>> times for
>>>>>> intra pair signals spectral lines may appear.
>>>>>>
>>>>>> Kind regards
>>>>>> Boris Traa
>>>>>> System design engineer EMC
>>>>>>
>>>>>> It's the currents that make circuits work or fail.
>>>>>>
>>>>>> Philips Innovation Services/EMC center
>>>>>> Room 2.020
>>>>>> High Tech Campus 26
>>>>>> 5656AE Eindhoven, The Netherlands
>>>>>> Tel: ++ 31 40 27 43766
>>>>>> Fax: ++ 31 40 27 42224
>>>>>> E-mail: boris.traa@xxxxxxxxxxx
>>>>>>
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: si-list-bounce@xxxxxxxxxxxxx
>>>>>> [mailto:si-list-bounce@xxxxxxxxxxxxx] On
>>>>>> Behalf Of Zhenwei Wang (zhenwwan)
>>>>>> Sent: Thursday 24 May 2012 4:05 AM
>>>>>> To: ah.vinod@xxxxxxxxx; SI-LIST
>>>>>> Subject: [SI-LIST] 答复: HDMI Frequency Failing RE Test by 7dB!!!!
>>>>>>
>>>>>> Hi Vinod,
>>>>>> I went through the email about your issue. Yes, if the pixel
>>>>>> clock is
>>>>>> 74.25Mhz, the data rate is ten times of pixel clock, equal 742.5Mhz.
>>>>>> Conceptually, TMDS signal have a virtual AC ground. So there is no DC
>>>>>> current requirement through ground pin. My suggestion: you should
>>>>>> check the
>>>>>> parameter "inter pair skew" of each differential data line.
>>>>>>
>>>>>> BR
>>>>>> Zhenwei(Jason) Wang
>>>>>> Cisco Systems (Shanghai) Video Technology Co., Ltd.
>>>>>>
>>>>>>
>>>>>> -----邮件原件-----
>>>>>> 发件人: si-list-bounce@xxxxxxxxxxxxx
>>>>>> [mailto:si-list-bounce@xxxxxxxxxxxxx] 代表
>>>>>> vinod ah
>>>>>> 发送时间: 2012年5月23日 21:58
>>>>>> 收件人: SI-LIST
>>>>>> 主题: [SI-LIST] HDMI Frequency Failing RE Test by 7dB!!!!
>>>>>>
>>>>>> Hi All,
>>>>>>
>>>>>> I am designing a board with HDMI input and HDMI output. I am facing
>>>>>> EMI
>>>>>> issue at 742.5MHz (failing FCC limits by 7dB) when running 1080p30 on
>>>>>> both
>>>>>> Input and output HDMI i.e. BLu ray player connected to HDMI input
>>>>>> connector
>>>>>> of my board is giving out data at 1080p30 and HDMI out of my board is
>>>>>> connected to TV which is also 1080p30 content. So i am unable to find
>>>>>> out
>>>>>> how is 742.5MHz coming out as radiation as it is 10th Harmonic of
>>>>>> pixel
>>>>>> clock 74.25MHz!!!!!!!. I am not facing any issues with other
>>>>>> harmonics
>>>>>> except for this. So i am totally confused on how to go about debugging
>>>>>> this
>>>>>> issue.
>>>>>>
>>>>>> Note: All the signals are routed on top layer without vias and all
>>>>>> signals
>>>>>> have solid ground plane reference. The blu ray player and TV used, is
>>>>>> tested
>>>>>> for radiation and no significant levels seen.
>>>>>>
>>>>>> Regards
>>>>>> Vinod A H
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>>>>
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