Line-Blanking interval of AD7390's output

According to the table 1-1 in ITU-R BT.470-6,  the line-blanking interval of PAL B/D/H/I/K/L should be 12us:

   

But when I measure  the output of ADV7390, I found that it is about 10us.  I have config ADV7390 by using the scripts in table 82.  I think this is correct for ADV7390 when the input is set to BT656, because according to figure 104 in datasheet, the line-blanking interval should be 288 clock ( frequency is 27MHz and period is 37.037ns)  , that is 288 x 37.037 = 10.6us.

But it is not conform to th BT470, and have ariased problems in some monitors ( most monitor  is OK).  How can I changed the line blanking interval to 12us?

  • Hi,

    Please check whether the below thread would help you.

    https://ez.analog.com/thread/51268

    Best Regards,

    Jeyasudha.M

  • Dear Jeyasudha.M,

            Thank you for your quick reply.  I have check that thread but it is not my case. The input clock of ADV7390 in my system is 27MHz.  I searched in the datasheet and found that bit3 of Reg#0x84(SD active video length)  can solve this problem. When setting active pixel to 702 pixel  by enable this bit,  the line-blanking interval is exactly 12us now. But I worry that the angle of view will be incorrect because the camera output 720 pixel and ADV7390 discard 18 of them. Should I add a scaler before AD7390 to scale 720 pixel down to 702 pixel?  Could you explain this bit in detail ? For example, how it is implement,  discard pixel or scale-down in AD7390?  In what circumstance I  should enable it, and  if it is enable , any other reigster should  be changed?  and so on.  Thanks in advance.

  • Hi chiguoqan,

    Setting the SD active video length bit to 1 will reduce the horizontal pixel length from 720 to 702 for PAL video. No other bit needs to be set for this functionality to be enabled. There is no scaler in the ADV7390, so these 18 pixels are essentially discarded. A scaler could be used before the encoder if you require all active video to be shown, but this is not essential.

    Since you mentioned you were using a camera as an input, it might be worth checking that the pixel clock frequency is 27MHz as some cameras give out a 28.375 MHz pixel clock, which the encoder cannot support. See the EngineerZone link attached for information regarding this:

    [ADV7391] PAL Output 

    Best Regards,

    Anthony

  • Hi,

    You did not react to sentence.

    I think this is correct for ADV7390 when the input is set to BT656, because according to figure 104 in datasheet, the line-blanking interval should be 288 clock ( frequency is 27MHz and period is 37.037ns)  , that is 288 x 37.037 = 10.6us.

    Do you confirm this ?

    In square pixel, the problem does not exist :

    (344+4+4)*1/29.5Mhz = 11.93µs.

    Regards,

    Perry,

  • So is this normal ADV7390 behaviour or is this a problem at BT656 generation ?