[SI-LIST] 答复: 答复: HDMI Frequency Failing RE Test by 7dB!!!!
- From: "Zhenwei Wang (zhenwwan)" <zhenwwan@xxxxxxxxx>
- To: "Traa, Boris" <boris.traa@xxxxxxxxxxx>, <ah.vinod@xxxxxxxxx>, "SI-LIST" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 24 May 2012 17:11:26 +0800
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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