ADV7281M MIPI OUTPUT signal only has brightness ,no color

Hi,

  Please ensure with below things,

      1. Kindly check whether the Crystal/Oscillator is outputting 28.63636MHz.

      2. Check if the FSC_lock bit (User Map register 0x10 bit[2]) is high. This bit indicates that the ADV728x has locked correctly to the color subcarrier.

      3. ADV728x may not work for poor video signals. If the color burst is below that percentage of the standard's value then the color will be killed, this will happen due to weak signal. If the color subcarrier is below 14.275mVpp, then the ADV728x will not be able to lock to the color subcarrier and it will output a black and white image.

      Please disable or change the threshold for the color kill function. The color kill function forces the ADV728x into black and white or grey output if the amplitude of the color subcarrier is too small.

     Kindly note that, 'CKILLTHR[2:0]' bits allow the user to select a threshold for the color kill function. The threshold applies only to QAM-based (NTSC and PAL) or FM-modulated (SECAM) video standards.

     To enable the color kill function, the CKE bit must be Set (CKE, Address 0x2B[6]). For the 000, 001, 010, and 011 settings, chroma demodulation inside the ADV728x may not work satisfactorily for poor input video signals So accordingly change the CKILLER register.

Note: The color kill algorithm can be disabled or its threshold set at a higher value.
          If color kill is enabled and the color carrier of the incoming video signal is less than the threshold for 128 consecutive video lines, color processing is switched off (black and white output).
          To switch the color processing back on, another 128 consecutive lines with a color burst greater than the threshold are required.

          If the amplitude of the color subcarrier is too low then the ADV7280 will never be able to lock to it. They could try using an amplifier to boost the signal. Also try replacing the resistor divider circuit on the ADV7280 with a single 75 Ohm resistor to ground. This will increase the amplitude of the signal to the ADV7280.

Thanks,

Poornima

Hi,

 Kindly note that, If you are not using a standard CVBS signal then it cannot be guaranteed that the ADV728x will lock to it so please check the 'FSC_LOCK' bit and it indicates that the ADV728x has locked to the color bust. It is a more reliable indication that the ADV728x has locked to a color burst.

1. If you have any external low pass filtering blocks connected to the input to the ADV728x, kindly remove them. These filters could be attenuating the higher frequency color information. Note that the ADV728x has an internal low pass filter with a 10Mhz cutoff (Please check the "Antialias filters" section of the ADV728x hardware manual).

2. Also, Try to force your backend SOC that is receiving the output from the ADV728x to only output video when the 'IN_LOCK and FSC_LOCK' bits are high.

3. Try adjusting the chroma filter controls and turn off the chroma AGC and manually change the chroma gain control register, CMG[11:0], until the chroma level matches that measured directly from the source.

4.Try to force the "Autodetect enable" bits (User Map register 0x07)" according to the PAL(PAL-I, PAL-60, PAL-M etc) /NTSC standard.

Note: If the amplitude of the color subcarrier is too low then the ADV728x will never be able to lock to it. Then could try using an amplifier to boost the signal. Also try replacing the resistor divider circuit on the ADV728x with a single 75 Ohm resistor to ground. This will increase the amplitude of the signal to the ADV728x.

Thanks,

Poornima