Ah, hello 742.5MHz my old friend. Alfred’s analysis in his email is good especially regarding frame rate. If you look in the 1.4 HDMI standard in section 5.1.2 you can see that the “vertical blanking” period consists of 45 lines. A breakdown of what’s contained within follows below that section. You can conduct further analysis of this period by using an FFT function on a high bandwidth digital scope (although you may struggle with the lower number of samples available in this target block) to narrow in on which part of the signal is causing you issues.
As for the frequency: 1080p/50Hz resolution uses a clock frequency of 148.5MHz. The three data pairs frequency is 5 x f_clk = 742.5MHz. Expect to see multiples of the clock at 445.5, 594 and 891MHz and plenty of emissions above 1GHz at 1485, 2227.5, 2970MHz, etc. 1080i/50Hz and 720p/50Hz resolution uses clock of 74.25MHz and data of 371.25 MHz It is this data fundamental that causes many of the radiated emissions problems associated with HDMI. This can be caused by poor signal integrity, mainly uneven tr/tf within each half of the differential pair. Possible solutions involve playing around with the pre-emphasis and drive strength register settings within the silicon, remembering to verify the signal integrity if you’ve found a combination that seems to work. Inline common mode chokes sometimes help at frequencies above 1GHz but more often not at these “lower” frequencies in the HDMI interface. Your best bet is carefully selecting a HDMI cable that has good shielding termination between cable screen and backshell. This is mostly a case of trial and error when purchasing from catalogs (forget eBay or Amazon here) or working with the cable vendor (e.g. Molex, Amphenol, Palpilot – other reputable cable vendors are available) to specify a decent quality cable. Cut open a $1 cable from Amazon and marvel at the internal construction! I hope this helps, Best of luck James From: Brent DeWitt [mailto:[email protected]] Sent: 15 October 2016 23:58 To: [email protected] Subject: [PSES] HDMI questions I’ve been working with some Silicon Images (Lattice Semi) 9777 multiplexer chips lately and would appreciate any insight list members might have. When used at any resolution below 4k, there seems to be a 10 dB emission “pedestal” that stands out of the baseline emission at several frequencies, 742 MHz in particular. The pedestal is 666 usec long and repeats at whatever frame rate is selected. At first, I thought it was correlated with the SPI bus activity, since the timing was identical, but further experiments show that not to be true. My question is, is this inherent to HDMI, or to the 9777? As is probably obvious, I don’t have a whole lot of experience with HDMI video. Thanks all! Brent DeWitt, AB1LF Milford, MA [https://ipmcdn.avast.com/images/icons/icon-envelope-tick-round-orange-animated-tick-v1.gif]<https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient&utm_term=icon> Virus-free. www.avast.com<https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient&utm_term=link> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]<mailto:[email protected]>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe)<http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]<mailto:[email protected]>> Mike Cantwell <[email protected]<mailto:[email protected]>> For policy questions, send mail to: Jim Bacher <[email protected]<mailto:[email protected]>> David Heald <[email protected]<mailto:[email protected]>> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
