ADV7393 CVBS Chroma level problem

1. Design goals

I am using FPGA and ADV7393 design a CVBS generator, FPGA output 8bit YCbCr + Hs + Vs signal to the ADV7393.

The generator output a CVBS signal, the format is PAL-D, the content is 100% color bar picture.

The generator is required to comply with the Chinese video standard(GB-3174-1995 PAL-D), which is required to be measured using the NI PXI-2172 after the completion of the design. The metering item is the brightness level and chroma level of each color signal, The standard value is as follows, the error range is less than -3% to + 3%.

WHITE YELLOW CYAN GREEN MAGENTA RED BLUE BLACK
brightness level(mv) 700 620 490 410 289 290 79 0
chroma level(mv) 627 885 827 827 885 627 0

2. My Design

FPGA produces 576I video timing and color RGB data, RGB data range is 16 ~ 235, FPGA internal design has a RGB to YCbCr module, conversion formula is as follows. And then YCbCr conversion 422 format, and finally the YCbCr422 data along with the video timing output to the ADV7393,

2.1 RGB to YCbCr

 Y = 0.299R + 0.587G + 0.114B
 Cb = -0.168736R - 0.331246G + 0.5B + 128
 Cr = 0.5R - 0.418688G - 0.081312B + 128

RGB = 16~235

2.2 VIDEO timming

Hs = 63   Hbp = 69   Hfp = 12  HdNum = 720      HsPOL=0

Vs  = 3     Vbp= 19    Vfp = 2     VdNum = 576     VsPOL=0

Interlace  

2.3 ADV7393 config

REG0x17 = 0x02          // software reset

REG0x00 = 0x1C         // all DAC on, PLL on

REG0x01 = 0x00          // SD input 

REG0x87 = 0x20           // SD input standard autodetection

REG0x80 = 0x11           //  SD standard: PAL B, PAL D, PAL G, PAL H, PAL I

REG0x82 = 0xC3

REG0x88 = 0x00            // 8-bit YCbCr input

REG0x8A = 0x0C           // slave mode    SD timing mode=mode2

REG0x8C = 0xCB           // Subcarrier Frequency

REG0x8D = 0x8A

REG0x8E = 0x09

REG0x8F = 0x2A

3. The problem

CVBS output connected to the TV, the TV normal recognition of the PAL signal, and the display of the color bar picture looks completely normal, but when use NI PXI-2172 to measure the chroma level found that the overall low tens of mv (red font number). The result of brightness level is normal (the number of the blue font).

WHITE YELLOW CYAN GREEN MAGENTA RED BLUE BLACK
brightness level(mv)

700  

698

620

617

490  

485

410  

405

289  

287

290  

207

79  

76.3

0

0

chroma level(mv)

627

566

885

801

827

755

827

748

885

804

627

570

0

4. Problem analysis

I think the problem is likely to be RGB to YCbCr formula, especially the Cr formula and Cb formula.

Does anyone help me analyze where my problem is?

 

attachment.pdf
  • The color space conversion reference formulas are pulled directly form industry standard specifications.  The ADV7393 passed vectorscope testing during initial chip bring up.

    1) Make sure there is no roll off associated with the circuitry connected to the ADV7393 outputs at the color carrier frequency.  

    2) If you believe the CSC coefficients are wrong you can configure the device with manual coefficients of you own design.