AnsweredAssumed Answered

AD9983A noise

Question asked by lionel.deflandre@silica.com on Oct 15, 2012
Latest reply on Jan 16, 2013 by DaveD

we have a vision system which is able to interface up to six
black&white analog industrial cameras.

Each camera in connected to one of the three primary
input of the ADC AD9983A. The secondary inputs are not used then tied to the
ground through a 75Ohm resistor.

 

We’re using the internal PLL to generate a clock synchronized with the
incoming video. The pixel clock is around 30MHz

. The ADC is configured in 4:4:4 mode, no DDR. ADC power supplies are
generated from a +5V power supply, through several low noise LDO.

 

The converted video from the “Red” and “Green” are OK, but the “Blue” channel is not OK, we have a
spatial noise on one pixel on two, each line, that could be seen on the
Channel3_noise.jpg image. There is a difference of 5 to 6 LSB between
contiguous pixels…which seems to be independent of the pixel values.

 

As I said before, we have two AD9983A ADCs on each board, and the
problem is observed on both “blue” channels. It is also seen on several boards.

 

The ADC internal register configuration is in here

00 - ChipRevision       : 00    

   01 - PllDivMsb          : 3b    

   02 - PllDivLsb          : 00    

   03 - VcoCpmp            : 60    

   04 - PhaseAdjust        : 80    

   05 - Gain[R][0]         : 40    

   06 - Gain[R][1]         : 00    

   07 - Gain[G][0]         : 40    

   08 - Gain[G][1]         : 00    

   09 - Gain[B][0]         : 40    

   0A - Gain[B][1]         : 00    

   0B - Offset[R][0]       : 40    

   0C - Offset[R][1]       : 00    

   0D - Offset[G][0]       : 40    

   0E - Offset[G][1]       : 00    

   0F - Offset[B][0]       : 40    

   10 - Offset[B][1]       : 00    

   11 - SyncSeparator      : 20    

   12 - HSyncControl       : 10    

   13 - HsyncPulseWidth    : 66    

   14 - VSyncControl       : 10    

   15 - VsyncPulseWidth    : 0a    

   16 - PreCoast           : 00    

   17 - PostCoast          : 00    

   18 - ClampCoastCtrl     : f0    

   19 - ClampPlacement     : 08    

   1A - ClampDuration      : 20    

   1B - ClampAndOffset     : 5b    

   1C - TestReg0           : ff    

   1D - SogControl         : 79    

   1E - Power              : 84    

   1F - OutputSelect1      : 94    

   20 - OutputSelect2      : 05    

   21 - Reserved21         : 20    

   22 - Reserved22         : 32    

   23 - SyncFilterWindow   : 0a    

   24 - SyncDetect         : 8d    

   25 - SyncPolarityDetect : 7d    

   26 - HsyncPerVsync[0]   : 04    

   27 - HsyncPerVsync[1]   : 00    

   28 - TestReg1           : bf    

   29 - TestReg2           : 02    

   2A - TestReg3           : 00    

   2B - TestReg4           : 00    

   2C - OffsetHold         : 00    

   2D - TestReg5           : e8    

   2E - TestReg6           : 20    

   34 - SogFilter          : 00    

   36 - VcoGear            : 00    

   3C - AutoGain           : 00

 

 

To isolate the source of the problem I have done some tests :

I have connected the analog inputs 2 and 3 together to the same camera
output. The image obtained from channel 2 is OK but the one from channel 3
isn’t. So I guess that the problem is not related to my PCB on the analog side.

Still with analog inputs 2 and 3 connected together, I put the channel 2
outputs on the channel 3 PCB trace (I have adaptation resistors on each line so
it’s quite easy to do this). Both channel 2 and 3 are then OK!! So it’s not due
to the PCB traces on the digital side!!

So it remains the ADC…that’s why I’m contacting you to get some support!
I have some doubts about the ouput formatter (4:4:4 or DDR 4:2:2 etc etc)…

For your information, on the previous design we used the AD9888 and had
no problem.

Outcomes