[SI-LIST] Re: HDMI Frequency Failing RE Test by 7dB!!!!
- From: Alexandre Desnoyers <alex@xxxxxxxx>
- To: ah.vinod@xxxxxxxxx
- Date: Thu, 24 May 2012 12:06:53 +0200
Hi Vinod,
Your mention below that your board is powered from an external AC-DC
adapter made me think that you should also check the radiation coming
from your PDN coupling onto the power cable. The radiation pattern that
you see when connecting/disconnecting the I/O cables may be caused by
the presence or absence of input clock+data, limiting the toggling of
your IC I/Os or internal logic. Do you have a ferrite bead or an EMI
filter right next to your PCB DC input? Is your decoupling done properly?
Good luck.
Alexandre Desnoyers
Electronic Design Engineer
Qtechnology A/S
Valby Langgade 142, 1.sal - 2500 Valby - Denmark - www.qtec.com
vinod ah wrote:
> Forgot to mention that, my board is powered from DC adapter which
> takes AC input and gives 12V DC output.
>
> On Wed, May 23, 2012 at 9:35 PM, vinod ah<ah.vinod@xxxxxxxxx> wrote:
>> 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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