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TVP5150AM1 AGC disabled gain

tetsu K
Prodigy 30 points
Other Parts Discussed in Thread: TVP5150AM1

Dear, everybody.

I am using TV5150AM1 to my designed board.
Video signal is NTSC-J or NTSC-M.
I have questions about my subject.


(1)
I change the following register, I set AGC disabled.
Analog Channel Controls Register(Adress 0x01) -> 0x14

After setting, I read Status Register#3(Adress 0x8A).
The register's data is 0x1A, is this value nominal gain?
I saw the following forum.

http://e2e.ti.com/support/data_converters/videoconverters/f/376/p/95771/334038.aspx#334038

Are nominal gain same in all TV5150AM1's lot?
Are 0x1A same in all TV5150AM1's lot?

If nominal gain is not Status Register#3,
could you please tell me about the gain?
I couldn't look for the gain in datasheet.


(2)
I would like to change gain from nominal gain to other gain,
when I set AGC disabled.
Could you please tell me how to set registers?

  • 0
    TI__Mastermind 43875 points

    Not using the AGC is not recommended.

    There is a difference between freezing the AGC and disabling the AGC.

    Freezing the AGC will maintain the currently determined settings and will depend on many factors.

    The status registers return the current settings as determined by the AGC processing.

    What are you actually trying to achieve?

    BR,

    Steve

  • 0 in reply to Steve Clynes
    Prodigy 30 points

    Dear Steve,

    Thank you for your replay.

    I understand a defference between disabling AGC and freezing the AGC.
    In the my system, I must control gain.
    If I use AGC, I cannot control gain that I want to set.
    So freezing the AGC cannot control gain too, I don't use freezing the AGC,
    I use disabling AGC.
    Could you please help me about how to set gain.

    I understood your explanation that the status register#3 isn't nominal gain (0x1A).
    If I mistake about that, could you please tell me about nominal gain.

    I think that the nominal gain is same by lot.
    But I afraid that the nominal gain vary by lot.

    best regard,
    tetsu

  • 0 in reply to tetsu K
    TI__Mastermind 43875 points

    Can you please explain more why you need to control the gain?

    Be aware that the gain affects more than just the brightness and contrast, it affects the entire input signal and if the AGC is not allowed to run then the sync levels and color burst measurements will not be correct.

    Manual gain control is not a supported mode of operation.

    If you can explain in more detail what you are actually trying to achieve I can probably help you find the correct solution.

    The nominal gain can and will vary based on many different factors, most related to the source signal, but some relate to the specific chip characteristics of the ADC.

    BR,

    Steve

  • 0 in reply to Steve Clynes
    Prodigy 30 points

    Dear Steve,

    I'm sorry, I am not good explanation.

    My system is mesurement machin using monochrome ccd camera.
    A optical source is laser.
    The system calcuate by ccd signal.

    I change optical intensity from micro controller unit's DAC.
    The DAC signal input to laser driver, and laser power changes the power to I want to set.

    When I set DAC, TVP5150AM1 digital output want be always same.
    For example,
    DAC 0x00 is VIDEO DATA about 0x00
    DAC 0x40 is VIDEO DATA about 0x40
    DAC 0x80 is VIDEO DATA about 0x80
    DAC 0xF0 is VIDEO DATA about 0xF0

    If I use AGC, VIDEO DATA is defferent.
    When it's bright place , AGC gain will be low. but when it's dark place, AGC gain will be High.
    So VIDEO OUTPU is not same for same DAC, My system cannot mesure.
    If I can control gain, I think that it is possible like the example.

    If I cannot control gain but I use disable gain,
    I think the gain is always same by lot.
    I will change gain by ccd camera's manual gain.

    Could you please give me good advice?

  • 0 in reply to tetsu K
    TI__Mastermind 43875 points

    My recommendation is to disable luma peak processing, composite peak protection and color burst reference AGC.

    This will still leave the sync AGC active and will compensate for other system variations such as cable length/cable attenuation and other component tolerances in the system.

    With this configuration you should not see any variations in the AGC settings for a given camera input even when the image that the camera sees changes (you would not see variations previously anyhow unless something in the image caused the peak detectors to trigger or the color carrier changed)

    I would also try configuring in S-video mode but only using the luma channel if your camera is a monochrome camera. This will give you higher effective resolution since there will be no color carrier filtering.

    The AGC does NOT change the brightness/contrast (i.e. will not automatically brighten a dark image) and only tries compensate for non standard/non stable signals which cause either variations in the sync amplitude (which should not happen for a well behaved source), variations in the color carrier (again, which should not happen for a well behaved source) or over saturations of the signal (luma peaks/noise or excessive chroma saturation of bright colors, e.g. yellow)

    BR,

    Steve