[SI-LIST] 答复: 答复: 答复: HDMI Frequency Failing RE Test by 7dB!!!!
- From: "Zhenwei Wang (zhenwwan)" <zhenwwan@xxxxxxxxx>
- To: "Traa, Boris" <boris.traa@xxxxxxxxxxx>, "Long Yang" <long.0.yang@xxxxxxxxx>
- Date: Fri, 25 May 2012 10:58:33 +0800
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.
·¢¼þÈË: Traa, Boris [mailto:boris.traa@xxxxxxxxxxx]
·¢ËÍʱ¼ä: 2012Äê5ÔÂ24ÈÕ 18:22
ÊÕ¼þÈË: Zhenwei Wang (zhenwwan); Long Yang
³ËÍ: ah.vinod@xxxxxxxxx; SI-LIST
Ö÷Ìâ: RE: [SI-LIST] ´ð¸´: ´ð¸´: 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 <mailto: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: ´ð¸´: [SI-LIST] ´ð¸´: ´ð¸´: 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.
·¢¼þÈË: Long Yang [mailto:long.0.yang@xxxxxxxxx]
·¢ËÍʱ¼ä: 2012Äê5ÔÂ24ÈÕ 17:38
ÊÕ¼þÈË: Zhenwei Wang (zhenwwan)
³ËÍ: Traa, Boris; ah.vinod@xxxxxxxxx; SI-LIST
Ö÷Ìâ: Re: [SI-LIST] ´ð¸´: ´ð¸´: 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.
-----ÓʼþÔ¼þ-----
·¢¼þÈË: Traa, Boris [mailto:boris.traa@xxxxxxxxxxx]
·¢ËÍʱ¼ä: 2012Äê5ÔÂ24ÈÕ 16:34
ÊÕ¼þÈË: Zhenwei Wang (zhenwwan); ah.vinod@xxxxxxxxx; SI-LIST
Ö÷Ìâ: RE: [SI-LIST] ´ð¸´: 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 <tel:%2B%2B%2031%2040%2027%2043766>
Fax: ++ 31 40 27 42224 <tel:%2B%2B%2031%2040%2027%2042224>
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] ´ð¸´: 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.
-----ÓʼþÔ¼þ-----
·¢¼þÈË: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] ´ú±í
vinod ah
·¢ËÍʱ¼ä: 2012Äê5ÔÂ23ÈÕ 21:58
ÊÕ¼þÈË: SI-LIST
Ö÷Ìâ: [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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