LTSpice - how to simulate simple NTSC video signal

Discussion in 'Programmer's Corner' started by mpownby, Oct 10, 2016.

  1. mpownby

    Thread Starter New Member

    Oct 7, 2016
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    Greetings,

    I am trying to understand how a circuit works (attached schematic). I am pretty sure that it takes an NTSC video signal in as a source and a) separates out the sync, and b) can also decode manchester data on a per line basis. I am really curious to learn how this circuit works and think that maybe trying to simulate it in LTSpice may be helpful. I only want to simulate the resistor/transistor/cap stuff, once it gets to the TTL parts, I can take it from there. The problem is that I don't know how to create the voltage source that changes over time. I have a good grasp of how the NTSC voltage looks. I mainly just need some guidance on how to create a voltage source that fluctuates between 0, 0.3V, and 1V (should be close enough) depending on the current time. If anyone could point me toward a tutorial or example that does this, that would be awesome.

    I already found something here ( http://www.analog-innovations.com/subcircuits.html , VidGen link ) but have no clue how to use it and it seems to be just generating a single line. I want to generate the vsync pulse and a few visible lines and I don't need to mess with stuff like color burst.

    Any help would be appreciated.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Can't you use a PWL voltage source?
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,988
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    If you show the exact signal you want to generate, we can be more specific in our suggestions.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I'm curious as to why you wish to simulate NTSC, given that analogue TV transmission has ceased in most countries?
     
  5. Bordodynov

    Active Member

    May 20, 2015
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    See
    NTSC.png
     
  6. mpownby

    Thread Starter New Member

    Oct 7, 2016
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    Here is an example of the signal from my scope.
     
  7. mpownby

    Thread Starter New Member

    Oct 7, 2016
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    I do a lot of retro hobby work with laserdiscs (many of which were NTSC based) and arcade games.
     
  8. mpownby

    Thread Starter New Member

    Oct 7, 2016
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    0
    thanks! I'll see how far I can get with this attachment :)
     
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