• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 46 subscribers
  • Views 1590 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TVP5146M2: video quality issue

Giacomo Burdi
Prodigy 20 points
Part Number: TVP5146M2
Other Parts Discussed in Thread: TVP5160

Good Morning,

I'm using TVP5146M2 in my project and I'm having problems with image quality.

The defect is especially noticeable around the text. Please look at the following pictures:

Register settings are the default except:

REG 0x08 = 0x00 (Stop Band Luminance Filter)

REG 0x0E = 0x04 (Wideband Chrominance Filter)

REG 0x33 = 0x40 (ITU-R BT.656 with embedded sync)

REG 0x34 = 0x11 (Output Enable)

I tried to change the AFE / Luminance Processing Control / Chrominance Processing Control / CTI registers but did not get good results.

Some advice?

Thank you

Giacomo

 

  • 0
    TI__Mastermind 43875 points

    CVBS video is inherently low quality, so you will never get fantastic results, especially with a 2D filter. You can get significantly higher quality on things like text/static images with a 3D comb filter (e.g. TVP5160) but the cost/complexity goes up too.

    Having said this, the first 2 images look a little like your analog cable is not correctly impedance matched and there might be ringing in the analog domain. Try to make sure that your analog signal termination is 75R and that your cables are good quality 75R cables. For your testing make the cables as short as possible. If changing the cable length moves the 'shadows' then it is most certainly an impedance issue.

    The final image shows a great example of what is called 'dot crawl' or 'hanging dots' and is a result of the basics of CVBS video, where luma and chroma information are merged and encoded into a single signal. The only way to reduce/eliminate these types of artifacts is to move to a 3D comb filter. Having said this any ringing caused by a bad cable will then manifest more as hanging dots, so I would focus on making sure the cables and impedance are good/correct first.

    BR,

    Steve

  • 0 in reply to Steve Clynes
    Prodigy 20 points

    Dear Steve,
    Thank you very much for your reply.
    I tried to connect the CVBS signal directly to the chip pin with 75R to GND and 100nF series capacitor but the situation does not change.

    More tips?

    Thank you!

    Giacomo

  • 0 in reply to Giacomo Burdi
    TI__Mastermind 43875 points
    How long is the cable from your source to the chip input? Is it 75R coax?

    If you take the exact same source and cable and feed directly into a monitor do you see any of the same artifacts (note, a modern LCD TV is not a good sink since it may have a 3D comb filter. An old fashioned analog monitor is the best sink for this test).

    The artifacts in picture 3 cannot really be eliminated without using a different (higher quality) 3D comb filter. It is a limitation of 2D filters on CVBS video. (en.wikipedia.org/.../Dot_crawl)

    BR,
    Steve