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I am looking for an example of a video genlock pixel clock generate using a PLL synchronized to the video sync signals. Such things seem to be rather rare now as everything has moved to highly integrated parts designed for LCD displays.

My goal is to do a video overlay. To stop it juddering the clock of the microcontroller generating the overlay needs to be synchronized to the video clock. I found the AV9173 (or ICS9173 clone), which while not widely available does appear to do what I want. Unfortunately the datasheet is rather sparse (http://media.digikey.com/pdf/Data%20Sheets/IDT/AV9173-01.pdf) and refers to an "Application Brief (AB01)" which I can't find anywhere.


I found a solution in the EL4584/5, which offer various PLL locked pixel clocks and are somewhat available.

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    \$\begingroup\$ If you found a good solution then add an answer to your own question. \$\endgroup\$ – David May 26 '14 at 8:59
  • \$\begingroup\$ No don't do that. Instead, answer your own question. Answers go into answers, questions into questions. \$\endgroup\$ – dom0 Dec 23 '14 at 23:59
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I've used a Cypress PSOC for generating a video overlay. I couldn't phase-lock the pixel clock, but feeding a 24Mhz clock into a divide-by-three which is "jammed" between the end of one's scan line's data and the start of the next scan line's vertical sync yields an 8Mhz pixel clock with 1/3 pixel jitter. I think I used a PSOC with 4 digital blocks; one was an SPI slave block, one was a counter used for the pixel clock, one was used to feed the /CS input, and I think one to set the end of the scan line and mute disable the pixel clock until the next line. The code for each scan line had to load 16 pixels worth of data, wait until the SPI block got enabled, and then load the SPI block with one byte every 24 clock cycles until all required data was clocked out.

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If you're not constrained to very small size, you can roll your own. It takes a 74HC4046, a single-supply op amp to use as an integrator, a few counter chips to make a divide by n counter, and a VCXO. The only "odd" part is the VCXO, and these are probably available if you're using anything like a standard pixel rate.

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  • \$\begingroup\$ This will be for arcade systems, so 50-60Hz vertical clock and 15KHz or 24KHz horizontal clock. I'd rather just drop in an IC though, as I don't want to debug my own. Unless you have a nice working example... \$\endgroup\$ – user May 21 '14 at 14:34
  • \$\begingroup\$ What pixel rate? \$\endgroup\$ – WhatRoughBeast May 21 '14 at 16:19
  • \$\begingroup\$ And do you have a preference for SMT or through-hole parts? And finally, what is your original video source? If it's generated on a processor board within the game, I'd expect you could find the clock rate (or a multiple) on the board and export it. \$\endgroup\$ – WhatRoughBeast May 21 '14 at 16:29
  • \$\begingroup\$ I'm aiming to run at 27MHz. I don't mind either SMD or TH, but TH is preferred for easy construction. Video source is various arcade systems. They vary but you can assume they are all 15KHz and 50 to 60Hz. I will adapt timing on my micro automatically, I just need a reasonable PLL locked to the horizontal sync pulse. \$\endgroup\$ – user May 21 '14 at 16:46
  • \$\begingroup\$ I've given this a little thought, and I doubt that a VCXO is the way to go. The problem (as I see it) is that I very much doubt that arcade games are likely to use broadcast standard timing. So, you'd need a VCO with considerably wider frequency swing, and I have no idea how wide that would be. \$\endgroup\$ – WhatRoughBeast May 21 '14 at 20:53
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Try using the TI LMH1980. It's a great chip that will let you sync to (most) video formats! http://www.ti.com/product/lmh1980

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    \$\begingroup\$ That is only a video sync separator, not capable of generating a pixel clock. \$\endgroup\$ – user May 26 '14 at 8:49

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