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AD9388A Horizontal distortion

Question asked by stucarmichael on May 24, 2013
Latest reply on May 31, 2013 by DaveD

Hi,

 

We have started seeing a Horizontal video distortion on one of our products that contains an AD9388A.  We don't believe we've seen it on older boards.


The problem appears to exist on both component and RGB inputs. 

To test I've attached the VGA output of a PC (1280x720p) which is showing excel to generate a simple grid pattern.  I've captured a couple of images.

 

ad9388_2.JPG

If you look at row 9 of the excel window in the jpeg you can see the distortion quite clearly, it’s like the Horizontal sync is slightly off.  The distortion slowly rolls up or down the image depending on the source or resolution. 

 

Ad9388_3.JPG

We discovered that the QPUMP setting was set to manual so we changed the QPUMP to automatic mode.

From the settings file “Register 0x47 data 0x0A ; Enable Automatic PLL_Qpump and VCO Range”

This gave us a good improvement but there is still a slight distortion (now on row 10 of the excel window).

 

I've checked that the voltage rails are good, i tried gently adjusting the 1.8V rail with no effect.

I've checked my crystal circuit, tried different load capacitors and tried an oscillator with no effect.

Temperature does not appear to effect the board either.

 

We tried playing with other register settings but we’re stuck for clues as to what to check next, any suggestions?

 

Best Regards,

stu carmichael

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