[SI-LIST] Re: 答复: 答复: 答复: HDMI Frequency Failing RE Test by 7dB!!!!
- From: DAVID CUTHBERT <telegrapher9@xxxxxxxxx>
- To: ah.vinod@xxxxxxxxx
- Date: Wed, 30 May 2012 06:41:59 -0600
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.
> >>>
> >>>
> >>>
> >>> ·¢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
> >>>
> >>>
> >>>
> >>> 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
> >>> 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] ´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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> >
> >
> > --
> > Steve Weir
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