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TV_Out output of DM8148

Ashvin Geete
Prodigy 70 points

In one of our ongoing project we are using the TV_OUT video output for NTSC format.

our application is such that we need to split the TV screen to display the captured videos from 8 different camera input (CVBS),

while displaying the video, quality is not good and we are observing the flicker and blurring effects.

we are using following schematic design:

 

 

 

We can configure TV_OUT circuit in any desired mode as either Normal Mode (Internal amplifier) or bypass mode (using external amplifier OP-AMP) , in both case we have not observed any difference with display quality,

also we did one mistake in layout that the TV_OUT_Norm trace is not routed with 75 Ohm impedance , while all other traces are mounted with 75 Ohm impedance.

 Please analyse this issue.

 is it possible to simplify the circuit by only using the internal amplifier (normal mode)?

Thanks

 

 

  • 0
    TI__Mastermind 43875 points

    Please refer to section 8.10.2 in the datasheet for recommended configurations.

    Can you post a picture of the image you are trying to display (frame buffer dump would be best) and a picture of the monitor highlighting the regions of concern?

    BR,

    Steve

  • 0 in reply to Steve Clynes
    Prodigy 70 points

    Thanks Steve !

    please refer the image below , snapshot of the screen diplaying video which is captured from 8 different cameras.

    below :

    these are no such cases where a specific area of video is blurring, in fact the complete video is appeared as blurred,

    I also want clarity that in which case i should use either normal mode or bypass mode.

    can i use simple normal mode (internal amplifier/buffer).

    thanks

    Ashvin

     

  • 0 in reply to Ashvin Geete
    TI__Mastermind 43875 points

    It is very difficult to see any specific issues with this display.

    Don't forget that CVBS video is very low resolution and very low fidelity.

    Are you able to change the display to a single full screen source camera then compare the display to the camera connected directly to the display?

    Regarding whether to use the bypass mode or not, this is entirely up to you. Using the bypass mode and an external buffer allows a truly impedance matched signal chain which in some extreme cases can give slightly better signal integrity, but again the fact that this is CVBS video is most likely the limiting factor anyhow.

    Using an external buffer also means you can easily use an active filte4r rather than a passive filter. This is entirely a system cost/performance decision ony you can make.

    BR,

    Steve

  • 0 in reply to Steve Clynes
    Prodigy 70 points

    Thanks Steve

    BR ,

    Ashvin Geete