[SI-LIST] Re: 答复: 答复: 答复: HDMI Frequency Failing RE Test by 7dB!!!!
- From: vinod ah <ah.vinod@xxxxxxxxx>
- To: SI-LIST <si-list@xxxxxxxxxxxxx>
- Date: Mon, 28 May 2012 15:13:49 +0530
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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