ADV7123 video flicker

Hi,

We are having problem of Color and Flickering issue on VGA display. ADV7123 chip get RGB data and convert into analog data.

 

We have tried different Horizontal and Vertical timing to remove the flicker but the flicker either increase or decrease but not completely removed.  We have observed the same issue on LCD, but we have enabled ‘DE’ mode in LCD and flicker removed. If we ground the DE pin (pin 11) of ADV7123, picture does not appear, so it means ADV chip understand the DE pin status and act according, but image flicker on the VGA display.

 

Your valuable information will help me to debug the issue in right direction as we are struggling since last couple of days to remove flicker on VGA.

 

Please let me know if call or meeting is required for further detailed discussion.

 

Awaiting for your response soon.

 

Thanks & Regards,

Suresh

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  • 0
    •  Analog Employees 
    on Jan 1, 2017 5:22 PM

    What speed grade of the DAC that you are using and the value of the clock to DAC? Looking at your schematic, I am not sure why you have used a 3.3V as the reference voltage for the DAC. It is clearly stated in the data sheet that the reference voltage for the DAC is in the range from 1.12 V to 1.35 V with typical being 1.235 V. Ideally, we use the AD1580 device as the external voltage reference to drive the DAC.

    So can you have the BLANK# pin connected as earlier advised? Change the Vref to a value as explained above. Use the Rset value as earlier explained.

    Also looking at your schematic there is a 82.5 Ohm resistors in the path of the VSYNC/HSYNC to the connector and I am not sure why you would have this? Ideally you should be passing the VSYNC/HSYNC signals through an ultra-high speed buffers such as the NC7SZ125 rather than the 82.5 Ohm resistors.

    As to the clock signal line driving the DAC the signal line should be as clean as possible, meaning to remove the 0 Ohm resistor and ensure the PCB trace is short. It is quite possible now that by the use of the 0 Ohm resistor in the path of the clock line to DAC, you have introduced a via connection so that clock line goes through 2 different PCB layers.

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  • 0
    •  Analog Employees 
    on Jan 1, 2017 5:22 PM

    What speed grade of the DAC that you are using and the value of the clock to DAC? Looking at your schematic, I am not sure why you have used a 3.3V as the reference voltage for the DAC. It is clearly stated in the data sheet that the reference voltage for the DAC is in the range from 1.12 V to 1.35 V with typical being 1.235 V. Ideally, we use the AD1580 device as the external voltage reference to drive the DAC.

    So can you have the BLANK# pin connected as earlier advised? Change the Vref to a value as explained above. Use the Rset value as earlier explained.

    Also looking at your schematic there is a 82.5 Ohm resistors in the path of the VSYNC/HSYNC to the connector and I am not sure why you would have this? Ideally you should be passing the VSYNC/HSYNC signals through an ultra-high speed buffers such as the NC7SZ125 rather than the 82.5 Ohm resistors.

    As to the clock signal line driving the DAC the signal line should be as clean as possible, meaning to remove the 0 Ohm resistor and ensure the PCB trace is short. It is quite possible now that by the use of the 0 Ohm resistor in the path of the clock line to DAC, you have introduced a via connection so that clock line goes through 2 different PCB layers.

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