[SI-LIST] Re: HDMI Frequency Failing RE Test by 7dB!!!!
- From: vinod ah <ah.vinod@xxxxxxxxx>
- To: Ken Wyatt <ken@xxxxxxxxxxxxxxxx>
- Date: Wed, 23 May 2012 21:35:45 +0530
Hi,
I have enclosure which is plastic :-(. Can i connect the shield pins
to ground plane as i don't have metal enclosure. will this help?
Also i have a query on common mode current part of the analysis. As i
mentioned earlier, the radiation level drops by 5dB when i remove the
HDMI input cable (Blu ray output), while it only drops by 2dB when i
remove HDMI out cable (TV input ). But since both the connectors are
grounded in the same way and same cable is used, why is there a
difference in radiation levels drops? Is it really common mode current
issue?
Regards
Vinod A H
On Wed, May 23, 2012 at 9:31 PM, Ken Wyatt <ken@xxxxxxxxxxxxxxxx> wrote:
> Vinod,
> The connector shield pins should all be connected to the signal return
> plane. Don't use a ferrite as suggested. Then the connector shield itself
> needs to be connected on all sides (as practical) directly to the metal
> product enclosure. This will allow any common-mode currents to return to
> their source(s) back INSIDE the product, rather than leaking out along the
> outside of the cable shield, causing radiation. You may need a shim or
> fingerstock to provide this bonding to the enclosure. If the enclosure is
> non-conductive (plastic), then you are likely "hosed" and may have to resort
> to ferrite choke on each HDMI cable (at the product end).
>
> If you have a current probe, you'll be able to view these currents while you
> troubleshoot. Check my article on current probes in the March 2012 issue of
> Interference Technology...
>
> http://www.interferencetechnology.com/the-hf-current-probe-theory-and-application/
>
> Cheers, Ken
>
> _______________________
> Kenneth Wyatt
> Wyatt Technical Services LLC
> Woodland Park, CO
> Email Me! | Web Site | Blog
> Subscribe to Newsletter
> Connect with me on LinkedIn
>
> On May 23, 2012, at 9:48 AM, vinod ah wrote:
>
> Hi Ken,
>
> Sorry the wording were not proper. Here is the corrected one.
>
> I just checked the layout and found that there are four shield pins
> and we have used a zero ohms between shield pin and ground. Is this ok
> to do so or should i have
> solid ground connection to the shield pins. Also if i replace the zero
> ohms with ferrite bead, will it help?
>
> Regards
> Vinod A H
>
> On Wed, May 23, 2012 at 9:11 PM, vinod ah <ah.vinod@xxxxxxxxx> wrote:
>
> Hi Ken,
>
>
> I just checked the layout and found that there are four pins for
>
> connecting the shield pins to ground and we have used a zero ohms
>
> between shield pin and ground. Is this ok to do so or should i have
>
> solid ground connection to the shield pins. Also if i replace the zero
>
> ohms with ferrite bead, will it help?
>
>
> Regards
>
> Vinod A H
>
>
> On Wed, May 23, 2012 at 8:56 PM, Ken Wyatt <ken@xxxxxxxxxxxxxxxx> wrote:
>
> Vinod,
>
>
> Is the HDMI connector shield -directly- connected to the (metallic)
>
> enclosure? This should ideally be multiple connections. If the shield is
>
> floating or poorly connected, you'll get common-mode currents flowing along
>
> the outside of the HDMI cable shield.
>
>
> Have you measured the common-mode currents with a current probe?
>
> _______________________
>
> Kenneth Wyatt
>
> Wyatt Technical Services LLC
>
> Woodland Park, CO
>
> Email Me! | Web Site | Blog
>
> Subscribe to Newsletter
>
> Connect with me on LinkedIn
>
>
> On May 23, 2012, at 9:17 AM, vinod ah wrote:
>
>
> Hi Vijay,
>
>
> We have option to control the current and voltage swing. We tried
>
> both, without violating eye test, but still the i am seeing radiation
>
> at 742.5MHz. The radiation level keeps chnaging as i try with multiple
>
> cables. I found the best cable i had to be failing FCC limits by 7dB.
>
> I used some HDMI cable which are sold by big brands, but i was failing
>
> FCC by 12dB !!!.
>
>
> Hi Boris,
>
>
> We tested the Blu ray player and TV with same HDMI cable used for our
>
> board testing. the Blu ray player used is from Sony while the TV is
>
> from LG, we connected the blu ray player to TV using same HDMI cable
>
> and took the readings.
>
>
> Regards
>
> Vinod A H
>
>
> On Wed, May 23, 2012 at 8:43 PM, Traa, Boris <boris.traa@xxxxxxxxxxx> wrote:
>
>
> Dear Venod,
>
>
>
> You said that TV is oke and Blu Ray is tested. Seperately or as a
>
> combination with the same cables you also used to attach your board?
>
>
>
> 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 vinod ah
>
>
> Sent: Wednesday 23 May 2012 3:58 PM
>
>
> To: SI-LIST
>
>
> Subject: [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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