[SI-LIST] 答复: Re: 答复: 答复: 答复: HDMI Frequency Failing RE Test by 7dB!!!!
- From: "Zhenwei Wang (zhenwwan)" <zhenwwan@xxxxxxxxx>
- To: <ah.vinod@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 30 May 2012 16:35:49 +0800
Effective radiating loop area changed between overlap or not.
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30日 14:54
收件人: si-list@xxxxxxxxxxxxx
主题: [SI-LIST] Re: 答复: 答复: 答复: HDMI Frequency Failing RE Test by 7dB!!!!
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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