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%.
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
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).
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？
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.