ADV7401 Blocky Video

Hi,

 Are you able to get free run output without any issues?

 Are you giving input in video pixel input port?

Thanks,

Poornima

Hello Poornima,

Thank you for taking a look at my post.

I haven't check the freerun or sync signals after input video is not present.  Our software is set to blank the digital decoder output when the ADV7401 doesn't detect a valid input.

We are not using the video pixel input port.  I am not sure why the DE_IN net was brought out.  Sorry if this was misleading. 

Something we were not sure about is how to set unused pins.  There is a note for Table 4 that list a handful of analog pins and says to tie them to AGND.  However, what is the recommend way to set the digital?   Could leaving DCLK_IN and some of the other digital floating cause issues?

Thank you,
Matthew

Update:

Freerun works as expected. 

We jumped AGND to the all the floating analog pins as recommended, but this didn't improve the video quality.

Something else we noticed besides the choppy video is mosquito noise.  In other words, white dots appear randomly in the video.  I think this is coming from the ADV7401 out of the digital output because with a black VGA video input there are random digital pulses.  I would expect to see all 24 pixel data lines low.  Is there something I can look at to improve the analog to digital conversion? 

The analog red, green and blue look fairly clean on a scope.  I only observed a minor periodic 140mV peak-to-peak pulse that is probably from a switching regulator.  Cold spray does clear the sparkles up for a while.

Hi,

Please refer below expert comment for unused pins at ez.analog.com/.../17677
    DE_IN,DCLK_IN can be weakly pulled low.
    Output port pins can be left float open or floating
    Input pixel ports can be left floating

Note: There are specific layout guide lines for using the ADV7401 other than normal good layout  practice.
-           Keep trace lengths as  short as possible
-           Keep the XTAL close to  the package and XTAL traces as short as possible
-           Keep the external loop  filter components (connected to ELPF) on the same side of the board and as close  as possible to the part
-           Ensure that power  supply design minimizes EMC possibility
-           Use decoupling caps  near to the part on each supply to reduce low, mid and high freq  noise
I’ve attached our eval note for the ADV7401 board which includes schematics, layout and bill of  materials. You should use this as a reference when working on the  ADV7401 layout.ADV7403_EVAL_NOTE_MINI_REVA_aug_07.pdf

Refer here for Video drifting - https://ez.analog.com/video/f/q-a/7892/adv7401-video-drifting-rising-gnd-reference/13603#13603

Thanks,

Poornima

Hi,

Please refer below expert comment for unused pins at ez.analog.com/.../17677
    DE_IN,DCLK_IN can be weakly pulled low.
    Output port pins can be left float open or floating
    Input pixel ports can be left floating

Note: There are specific layout guide lines for using the ADV7401 other than normal good layout  practice.
-           Keep trace lengths as  short as possible
-           Keep the XTAL close to  the package and XTAL traces as short as possible
-           Keep the external loop  filter components (connected to ELPF) on the same side of the board and as close  as possible to the part
-           Ensure that power  supply design minimizes EMC possibility
-           Use decoupling caps  near to the part on each supply to reduce low, mid and high freq  noise
I’ve attached our eval note for the ADV7401 board which includes schematics, layout and bill of  materials. You should use this as a reference when working on the  ADV7401 layout.ADV7403_EVAL_NOTE_MINI_REVA_aug_07.pdf

Refer here for Video drifting - https://ez.analog.com/video/f/q-a/7892/adv7401-video-drifting-rising-gnd-reference/13603#13603

Thanks,

Poornima